Merge branch 'lukeshu/9p-read-iovec'HEADmain

35 files changed, 550 insertions, 256 deletions

diff --git a/CMakeLists.txt b/CMakeLists.txt
index 386b13c..b379a8f 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -98,6 +98,7 @@ function(add_lib_test arg_libname arg_testname)
 	if (ENABLE_TESTS)
 		add_executable("${arg_testname}" "tests/${arg_testname}.c")
 		target_link_libraries("${arg_testname}" "${arg_libname}")
+		target_include_directories("${arg_testname}" PRIVATE ${CMAKE_CURRENT_SOURCE_DIR}/tests)
 		add_test(
 			NAME    "${arg_libname}/${arg_testname}"
 			COMMAND valgrind --error-exitcode=2 "./${arg_testname}"
@@ -139,7 +140,7 @@ add_subdirectory(libobj)
 add_subdirectory(libcr)
 add_subdirectory(libcr_ipc)
 add_subdirectory(libhw_generic)
-add_subdirectory(libhw)
+add_subdirectory(libhw_cr)
 add_subdirectory(libdhcp)
 add_subdirectory(libusb)
 add_subdirectory(lib9p)
diff --git a/HACKING.md b/HACKING.md
index d522034..9e19c26 100644
--- a/HACKING.md
+++ b/HACKING.md
@@ -18,8 +18,8 @@ Our own tiny cooperative-multitasking OS:
  - `libcr/`: The kernel (a simple coroutine library)
  - `libcr_ipc/`: IPC primatives (semaphores, mutexes, channels, ...)
    for libcr
- - `libhw/`: The hardware drivers
  - `libhw_generic/`: The hardware abstraction layer
+ - `libhw_cr/`: The hardware drivers
 
 Libraries for generic parts of what the harness is doing:
 
diff --git a/cmd/sbc_harness/CMakeLists.txt b/cmd/sbc_harness/CMakeLists.txt
index d7923c2..fa42b47 100644
--- a/cmd/sbc_harness/CMakeLists.txt
+++ b/cmd/sbc_harness/CMakeLists.txt
@@ -24,7 +24,7 @@ target_link_libraries(sbc_harness_objs
 	libmisc
 	libusb
 	libdhcp
-	libhw
+	libhw_cr
 	lib9p
 	lib9p_util
 )
diff --git a/lib9p/include/lib9p/srv.h b/lib9p/include/lib9p/srv.h
index 83aabc0..ff5ebdc 100644
--- a/lib9p/include/lib9p/srv.h
+++ b/lib9p/include/lib9p/srv.h
@@ -37,53 +37,98 @@ int lib9p_srv_acknowledge_flush(struct lib9p_srv_ctx *ctx);
 
 /* interface definitions ******************************************************/
 
-#define lib9p_srv_file_LO_IFACE                                                 \
-	/* all - resource management */                                         \
-	LO_FUNC(void                       , free   ) /* must not error */      \
-	LO_FUNC(struct lib9p_qid           , qid    ) /* must not error */      \
-	LO_FUNC(uint32_t                   , chio   , struct lib9p_srv_ctx *,   \
-	                                              bool rd, bool wr,         \
-	                                              bool trunc)               \
-	                                                                        \
-	/* all - syscalls */                                                    \
-	LO_FUNC(struct lib9p_stat          , stat   , struct lib9p_srv_ctx *)   \
-	LO_FUNC(void                       , wstat  , struct lib9p_srv_ctx *,   \
-	                                              struct lib9p_stat new)    \
-	LO_FUNC(void                       , remove , struct lib9p_srv_ctx *)   \
-	                                                                        \
-	/* directories - base */                                                \
-	LO_FUNC(lo_interface lib9p_srv_file, dopen  , struct lib9p_srv_ctx *,   \
-	                                              struct lib9p_s childname) \
-	LO_FUNC(lo_interface lib9p_srv_file, dcreate, struct lib9p_srv_ctx *,   \
-	                                              struct lib9p_s childname, \
-	                                              lib9p_dm_t perm,          \
-	                                              lib9p_o_t flags)          \
-	                                                                        \
-	/* directories - once opened */                                         \
-	LO_FUNC(size_t /* <- obj cnt */    , dread  , struct lib9p_srv_ctx *,   \
-	                                              uint8_t *buf,             \
-	                           /* num bytes -> */ uint32_t byte_count,      \
-	             /* starting at this object -> */ size_t obj_offset)        \
-	                                                                        \
-	/* non-directories - once opened */                                     \
-	LO_FUNC(uint32_t                   , pread  , struct lib9p_srv_ctx *,   \
-	                                              void *buf,                \
-	                                              uint32_t byte_count,      \
-	                                              uint64_t byte_offset)     \
-	LO_FUNC(uint32_t                   , pwrite , struct lib9p_srv_ctx *,   \
-	                                              void *buf,                \
-	                                              uint32_t byte_count,      \
+lo_interface lib9p_srv_fio;
+lo_interface lib9p_srv_dio;
+
+/* FIXME: I don't like that the pointers returned by stat() and
+ * pread() have to remain live after they return.  Perhaps a
+ * `respond()`-callback?  But that just reads as gross in C.
+ *
+ * FIXME: It would be nice if pread() could return more than 1 iovec.
+ */
+#define lib9p_srv_file_LO_IFACE                                                \
+	/* resource management **********************************************/ \
+	                                                                       \
+	/**                                                                    \
+	 * free() is be called when all FIDs associated with the file are      \
+	 * clunked.                                                            \
+	 *                                                                     \
+	 * free() MUST NOT error.                                              \
+	 */                                                                    \
+	LO_FUNC(void                       , free   )                          \
+	                                                                       \
+	/**                                                                    \
+	 * qid() is called frequently and returns the current QID of the file. \
+	 * The .path field MUST never change, the .type field may change in    \
+	 * response to wstat() calls (but the QT_DIR bit MUST NOT change), and \
+	 * the .vers field may change frequently in response to any number of  \
+	 * things (wstat(), write(), or non-9P events).                        \
+	 *                                                                     \
+	 * qid() MUST NOT error.                                               \
+	 */                                                                    \
+	LO_FUNC(struct lib9p_qid           , qid    )                          \
+	                                                                       \
+	/* non-"opened" generic I/O *****************************************/ \
+	                                                                       \
+	LO_FUNC(struct lib9p_stat          , stat   , struct lib9p_srv_ctx *)  \
+	LO_FUNC(void                       , wstat  , struct lib9p_srv_ctx *,  \
+	                                              struct lib9p_stat new)   \
+	LO_FUNC(void                       , remove , struct lib9p_srv_ctx *)  \
+	                                                                       \
+	/* non-"opened" directory I/O ***************************************/ \
+	                                                                       \
+	LO_FUNC(lo_interface lib9p_srv_file, dwalk  , struct lib9p_srv_ctx *,  \
+	                                             struct lib9p_s childname) \
+	LO_FUNC(lo_interface lib9p_srv_file, dcreate, struct lib9p_srv_ctx *,  \
+	                                             struct lib9p_s childname, \
+	                                              lib9p_dm_t perm,         \
+	                                              lib9p_o_t flags)         \
+	                                                                       \
+	/* open() for I/O ***************************************************/ \
+	                                                                       \
+	LO_FUNC(lo_interface lib9p_srv_fio , fopen , struct lib9p_srv_ctx *,   \
+	                                                    bool rd, bool wr,  \
+	                                                    bool trunc)        \
+	LO_FUNC(lo_interface lib9p_srv_dio , dopen , struct lib9p_srv_ctx *)
+LO_INTERFACE(lib9p_srv_file);
+
+#define lib9p_srv_fio_LO_IFACE                                                 \
+	LO_FUNC(struct lib9p_qid           , qid    )                          \
+	LO_FUNC(void                       , iofree )                          \
+	LO_FUNC(uint32_t                   , iounit )                          \
+	LO_FUNC(void                       , pread  , struct lib9p_srv_ctx *,  \
+	                                              uint32_t byte_count,     \
+	                                              uint64_t byte_offset,    \
+	                                              struct iovec *ret)       \
+	LO_FUNC(uint32_t                   , pwrite , struct lib9p_srv_ctx *,  \
+	                                              void *buf,               \
+	                                              uint32_t byte_count,     \
 	                                              uint64_t byte_offset)
-LO_INTERFACE(lib9p_srv_file)
+LO_INTERFACE(lib9p_srv_fio);
+
+/* FIXME: The dio interface just feels clunky.  I'm not in a rush to
+ * change it because util9p_static_dir is already implemented and I
+ * don't anticipate the sbc-harness needing another dio
+ * implementation.  But if I wanted lib9p to be used outside of
+ * sbc-harness, this is one of the first things that I'd want to
+ * change.
+ */
+#define lib9p_srv_dio_LO_IFACE                                                 \
+	LO_FUNC(struct lib9p_qid           , qid    )                          \
+	LO_FUNC(void                       , iofree )                          \
+	LO_FUNC(size_t /* <- obj cnt */    , dread  , struct lib9p_srv_ctx *,  \
+	                                              uint8_t *buf,            \
+	                           /* num bytes -> */ uint32_t byte_count,     \
+	             /* starting at this object -> */ size_t obj_offset)
+LO_INTERFACE(lib9p_srv_dio);
 
 #define LIB9P_SRV_NOTDIR(TYP, NAM)                                                                                                                                       \
-	static lo_interface lib9p_srv_file NAM##_dopen  (TYP *, struct lib9p_srv_ctx *, struct lib9p_s)                        { assert_notreached("not a directory"); } \
+	static lo_interface lib9p_srv_file NAM##_dwalk  (TYP *, struct lib9p_srv_ctx *, struct lib9p_s)                        { assert_notreached("not a directory"); } \
 	static lo_interface lib9p_srv_file NAM##_dcreate(TYP *, struct lib9p_srv_ctx *, struct lib9p_s, lib9p_dm_t, lib9p_o_t) { assert_notreached("not a directory"); } \
-	static size_t                      NAM##_dread  (TYP *, struct lib9p_srv_ctx *, uint8_t *, uint32_t, size_t)           { assert_notreached("not a directory"); }
+	static lo_interface lib9p_srv_dio  NAM##_dopen  (TYP *, struct lib9p_srv_ctx *)                                        { assert_notreached("not a directory"); }
 
 #define LIB9P_SRV_NOTFILE(TYP, NAM) \
-	static uint32_t NAM##_pread (TYP *, struct lib9p_srv_ctx *, void *, uint32_t, uint64_t) { assert_notreached("not a file"); } \
-	static uint32_t NAM##_pwrite(TYP *, struct lib9p_srv_ctx *, void *, uint32_t, uint64_t) { assert_notreached("not a file"); }
+	static lo_interface lib9p_srv_fio  NAM##_fopen  (TYP *, struct lib9p_srv_ctx *, bool, bool, bool)                      { assert_notreached("not a file"); }
 
 /* main server entrypoints ****************************************************/
 
@@ -103,16 +148,32 @@ struct lib9p_srv {
 };
 
 /**
+ * In an infinite loop, accept a connection and read messages from it until
+ * close; dispatching requests to a pool of lib9p_srv_write_cr() coroutines
+ * with the same `srv`.
+ *
  * Will just close the connection if a T-message has a size[4] <7.
  *
+ * @param srv: The server configuration and state; has an associated pool of
+ *             lib9p_srv_write_cr() coroutines.
+ * @param listener: The listener object to accept connections from.
+ *
  * @errno LINUX_EMSGSIZE T-message has size[4] bigger than max_msg_size
  * @errno LINUX_EDOM Tversion specified an impossibly small max_msg_size
  * @errno LINUX_EOPNOTSUPP T-message has an R-message type, or an unrecognized T-message type
  * @errno LINUX_EBADMSG T-message has wrong size[4] for its content, or has invalid UTF-8
  * @errno LINUX_ERANGE R-message does not fit into max_msg_size
  */
-
 [[noreturn]] void lib9p_srv_read_cr(struct lib9p_srv *srv, lo_interface net_stream_listener listener);
+
+/**
+ * Service requests to the `struct lib9p_srv *srv` argument that have been
+ * read by lib9p_srv_read_cr().
+ *
+ * @param struct lib9p_srv *srv: The server configuration and state; has an
+ *                               associated pool of lib9p_srv_read_cr()
+ *                               coroutines.
+ */
 COROUTINE lib9p_srv_write_cr(void *_srv);
 
 #endif /* _LIB9P_SRV_H_ */
diff --git a/lib9p/srv.c b/lib9p/srv.c
index 2475baf..50d0b78 100644
--- a/lib9p/srv.c
+++ b/lib9p/srv.c
@@ -60,8 +60,7 @@ struct srv_pathinfo {
 	 * from FIDs. */
 	unsigned int                     gc_refcount;
 	/* References from fids with FIDFLAG_OPEN_R/FIDFLAG_OPEN_W.  */
-	unsigned int                     rd_refcount;
-	unsigned int                     wr_refcount;
+	unsigned int                     io_refcount;
 };
 
 #define NAME  pathmap
@@ -77,11 +76,18 @@ struct srv_pathinfo {
 #define FIDFLAG_OPEN   (FIDFLAG_OPEN_R|FIDFLAG_OPEN_W)
 
 struct _srv_fidinfo {
-	srv_path_t                       path;
-	uint8_t                          flags;
-	uint32_t                         iounit;
-	size_t                           dir_idx;
-	uint64_t                         dir_off;
+	srv_path_t                                      path;
+	uint8_t                                         flags;
+	union {
+		struct {
+			lo_interface lib9p_srv_fio              io;
+		}                                       file;
+		struct {
+			lo_interface lib9p_srv_dio              io;
+			size_t                                  idx;
+			uint64_t                                off;
+		}                                       dir;
+	};
 };
 
 #define NAME  fidmap
@@ -122,9 +128,9 @@ struct _srv_sess {
 	/* mutable */
 	bool                     initialized;
 	bool                     closing;
-	struct pathmap           paths;
-	struct reqmap            reqs;
-	struct fidmap            fids;
+	struct pathmap           paths; /* srv_path_t  => lib9p_srv_file + metadata */
+	struct fidmap            fids;  /* lib9p_fid_t => lib9p_srv_{fio,dio} + metadata */
+	struct reqmap            reqs;  /* lib9p_tag_t => *_lib9p_srv_req */
 };
 
 struct _lib9p_srv_req {
@@ -463,8 +469,7 @@ static inline struct srv_pathinfo *srv_util_pathsave(struct _lib9p_srv_req *ctx,
 				.file        = file,
 				.parent_dir  = parent_path,
 				.gc_refcount = 0,
-				.rd_refcount = 0,
-				.wr_refcount = 0,
+				.io_refcount = 0,
 			});
 		assert(pathinfo);
 		if (parent_path != qid.path) {
@@ -515,6 +520,12 @@ static inline struct _srv_fidinfo *srv_util_fidsave(struct _lib9p_srv_req *ctx,
 	struct _srv_fidinfo *fidinfo = fidmap_load(&ctx->parent_sess->fids, fid);
 	if (fidinfo) {
 		if (overwrite) {
+			struct srv_pathinfo *old_pathinfo = pathmap_load(&ctx->parent_sess->paths, fidinfo->path);
+			assert(old_pathinfo);
+			if (srv_util_pathisdir(old_pathinfo))
+				LO_CALL(fidinfo->dir.io, iofree);
+			else
+				LO_CALL(fidinfo->file.io, iofree);
 			srv_util_pathfree(ctx, fidinfo->path);
 		} else {
 			lib9p_error(&ctx->ctx.basectx,
@@ -748,7 +759,7 @@ static void handle_Twalk(struct _lib9p_srv_req *ctx,
 				break;
 			}
 
-			lo_interface lib9p_srv_file member_file = LO_CALL(pathinfo->file, dopen, &ctx->ctx, req->wname[resp->nwqid]);
+			lo_interface lib9p_srv_file member_file = LO_CALL(pathinfo->file, dwalk, &ctx->ctx, req->wname[resp->nwqid]);
 			assert(LO_IS_NULL(member_file) == lib9p_ctx_has_error(&ctx->ctx.basectx));
 			if (lib9p_ctx_has_error(&ctx->ctx.basectx))
 				break;
@@ -774,6 +785,13 @@ static void handle_Twalk(struct _lib9p_srv_req *ctx,
 		pathinfo = new_pathinfo;
 	}
 	if (resp->nwqid == req->nwname) {
+		if (req->newfid == req->fid) {
+			if (srv_util_pathisdir(pathinfo))
+				LO_CALL(fidinfo->dir.io, iofree);
+			else
+				LO_CALL(fidinfo->file.io, iofree);
+			fidinfo->flags = 0;
+		}
 		if (!srv_util_fidsave(ctx, req->newfid, pathinfo, req->newfid == req->fid))
 			srv_util_pathfree(ctx, LO_CALL(pathinfo->file, qid).path);
 	} else {
@@ -816,7 +834,6 @@ static void handle_Topen(struct _lib9p_srv_req *ctx,
 	/* Variables.  */
 	lib9p_o_t       reqmode  = req->mode;
 	uint8_t         fidflags = fidinfo->flags;
-	uint32_t        iounit   = fidinfo->iounit;
 
 	/* Check permissions.  */
 	if (reqmode & LIB9P_O_RCLOSE) {
@@ -831,13 +848,13 @@ static void handle_Topen(struct _lib9p_srv_req *ctx,
 			            LINUX_EACCES, "permission denied to remove-on-close");
 			return;
 		}
-		fidflags = fidflags | FIDFLAG_RCLOSE;
+		fidflags |= FIDFLAG_RCLOSE;
 	}
 	struct lib9p_stat stat = LO_CALL(pathinfo->file, stat, &ctx->ctx);
 	if (lib9p_ctx_has_error(&ctx->ctx.basectx))
 		return;
 	lib9p_stat_assert(stat);
-	if ((stat.file_mode & LIB9P_DM_EXCL) && (pathinfo->rd_refcount || pathinfo->wr_refcount)) {
+	if ((stat.file_mode & LIB9P_DM_EXCL) && pathinfo->io_refcount) {
 		lib9p_error(&ctx->ctx.basectx,
 		            LINUX_EEXIST, "exclusive file is already opened");
 		return;
@@ -870,26 +887,36 @@ static void handle_Topen(struct _lib9p_srv_req *ctx,
 	}
 
 	/* Actually make the call.  */
-	if ((reqmode & LIB9P_O_TRUNC) || (rd && !pathinfo->rd_refcount) || (wr && !pathinfo->wr_refcount) ) {
-		iounit = LO_CALL(pathinfo->file, chio, &ctx->ctx,
-		                 fidflags & FIDFLAG_OPEN_R,
-		                 fidflags & FIDFLAG_OPEN_W,
-		                 reqmode & LIB9P_O_TRUNC);
+	uint32_t iounit;
+	struct lib9p_qid qid;
+	if (srv_util_pathisdir(pathinfo)) {
+		fidinfo->dir.io = LO_CALL(pathinfo->file, dopen, &ctx->ctx);
+		assert(LO_IS_NULL(fidinfo->dir.io) == lib9p_ctx_has_error(&ctx->ctx.basectx));
+		if (lib9p_ctx_has_error(&ctx->ctx.basectx))
+			return;
+		fidinfo->dir.idx = 0;
+		fidinfo->dir.off = 0;
+		qid = LO_CALL(fidinfo->dir.io, qid);
+		iounit = 0;
+	} else {
+		fidinfo->file.io = LO_CALL(pathinfo->file, fopen, &ctx->ctx,
+		                           rd, wr,
+		                           reqmode & LIB9P_O_TRUNC);
+		assert(LO_IS_NULL(fidinfo->file.io) == lib9p_ctx_has_error(&ctx->ctx.basectx));
 		if (lib9p_ctx_has_error(&ctx->ctx.basectx))
 			return;
+		qid = LO_CALL(fidinfo->file.io, qid);
+		iounit = LO_CALL(fidinfo->file.io, iounit);
 	}
 
 	/* Success.  */
-	if (rd) {
-		fidflags = fidflags | FIDFLAG_OPEN_R;
-		pathinfo->rd_refcount++;
-	}
-	if (wr) {
-		fidflags = fidflags | FIDFLAG_OPEN_W;
-		pathinfo->wr_refcount++;
-	}
+	if (rd)
+		fidflags |= FIDFLAG_OPEN_R;
+	if (wr)
+		fidflags |= FIDFLAG_OPEN_W;
+	pathinfo->io_refcount++;
 	fidinfo->flags = fidflags;
-	resp->qid = stat.file_qid;
+	resp->qid = qid;
 	resp->iounit = iounit;
 }
 
@@ -923,7 +950,6 @@ static void handle_Tread(struct _lib9p_srv_req *ctx,
 	/* Variables.  */
 	struct srv_pathinfo *pathinfo = pathmap_load(&ctx->parent_sess->paths, fidinfo->path);
 	assert(pathinfo);
-	resp->data = (char *)(&resp[1]);
 
 	/* Do it.  */
 	if (srv_util_pathisdir(pathinfo)) {
@@ -931,16 +957,17 @@ static void handle_Tread(struct _lib9p_srv_req *ctx,
 		size_t idx;
 		if (req->offset == 0)
 			idx = 0;
-		else if (req->offset == fidinfo->dir_off)
-			idx = fidinfo->dir_idx;
+		else if (req->offset == fidinfo->dir.off)
+			idx = fidinfo->dir.idx;
 		else {
 			lib9p_errorf(&ctx->ctx.basectx,
 			             LINUX_EINVAL, "invalid offset (must be 0 or %"PRIu64"): %"PRIu64,
-			             fidinfo->dir_off, req->offset);
+			             fidinfo->dir.off, req->offset);
 			return;
 		}
 		/* Do it.  */
-		size_t num = LO_CALL(pathinfo->file, dread, &ctx->ctx, (uint8_t *)resp->data, req->count, idx);
+		resp->data = (char *)(&resp[1]);
+		size_t num = LO_CALL(fidinfo->dir.io, dread, &ctx->ctx, (uint8_t *)resp->data, req->count, idx);
 		/* Translate object-count back to byte-count.  */
 		uint32_t len = 0;
 		for (size_t i = 0; i < num; i++) {
@@ -950,10 +977,18 @@ static void handle_Tread(struct _lib9p_srv_req *ctx,
 		}
 		resp->count = len;
 		/* Remember.  */
-		fidinfo->dir_idx = idx+num;
-		fidinfo->dir_off = req->offset + len;
-	} else
-		resp->count = LO_CALL(pathinfo->file, pread, &ctx->ctx, resp->data, req->count, req->offset);
+		fidinfo->dir.idx = idx+num;
+		fidinfo->dir.off = req->offset + len;
+	} else {
+		struct iovec iov;
+		LO_CALL(fidinfo->file.io, pread, &ctx->ctx, req->count, req->offset, &iov);
+		if (!lib9p_ctx_has_error(&ctx->ctx.basectx)) {
+			resp->count = iov.iov_len;
+			resp->data = iov.iov_base;
+			if (resp->count > req->count)
+				resp->count = req->count;
+		}
+	}
 }
 
 static void handle_Twrite(struct _lib9p_srv_req *ctx,
@@ -979,7 +1014,7 @@ static void handle_Twrite(struct _lib9p_srv_req *ctx,
 	assert(pathinfo);
 
 	/* Do it.  */
-	resp->count = LO_CALL(pathinfo->file, pwrite, &ctx->ctx, req->data, req->count, req->offset);
+	resp->count = LO_CALL(fidinfo->file.io, pwrite, &ctx->ctx, req->data, req->count, req->offset);
 }
 
 static void clunkremove(struct _lib9p_srv_req *ctx, lib9p_fid_t fid, bool remove) {
@@ -1012,6 +1047,13 @@ static void clunkremove(struct _lib9p_srv_req *ctx, lib9p_fid_t fid, bool remove
 	}
 
  clunk:
+	if (fidinfo->flags & FIDFLAG_OPEN) {
+		if (srv_util_pathisdir(pathinfo))
+			LO_CALL(fidinfo->dir.io, iofree);
+		else
+			LO_CALL(fidinfo->file.io, iofree);
+		pathinfo->io_refcount--;
+	}
 	srv_util_pathfree(ctx, LO_CALL(pathinfo->file, qid).path);
 	fidmap_del(&ctx->parent_sess->fids, fid);
 }
diff --git a/lib9p/tests/test_server/CMakeLists.txt b/lib9p/tests/test_server/CMakeLists.txt
index 74a759d..5313917 100644
--- a/lib9p/tests/test_server/CMakeLists.txt
+++ b/lib9p/tests/test_server/CMakeLists.txt
@@ -18,7 +18,7 @@ target_link_libraries(test_server_objs
 	libmisc
 	lib9p
 	lib9p_util
-	libhw
+	libhw_cr
 )
 
 # Analyze the stack ############################################################
diff --git a/lib9p/tests/test_server/main.c b/lib9p/tests/test_server/main.c
index 074dbe7..c759029 100644
--- a/lib9p/tests/test_server/main.c
+++ b/lib9p/tests/test_server/main.c
@@ -48,7 +48,10 @@ struct api_file {
 	uint64_t pathnum;
 };
 LO_IMPLEMENTATION_H(lib9p_srv_file, struct api_file, api)
+LO_IMPLEMENTATION_H(lib9p_srv_fio, struct api_file, api)
+
 LO_IMPLEMENTATION_C(lib9p_srv_file, struct api_file, api, static)
+LO_IMPLEMENTATION_C(lib9p_srv_fio, struct api_file, api, static)
 
 static void api_free(struct api_file *self) {
 	assert(self);
@@ -61,11 +64,6 @@ static struct lib9p_qid api_qid(struct api_file *self) {
 		.path = self->pathnum,
 	};
 }
-static uint32_t api_chio(struct api_file *self, struct lib9p_srv_ctx *ctx, bool, bool, bool) {
-	assert(self);
-	assert(ctx);
-	return 0;
-}
 
 static struct lib9p_stat api_stat(struct api_file *self, struct lib9p_srv_ctx *ctx) {
 	assert(self);
@@ -101,6 +99,21 @@ static void api_remove(struct api_file *self, struct lib9p_srv_ctx *ctx) {
 
 LIB9P_SRV_NOTDIR(struct api_file, api)
 
+static lo_interface lib9p_srv_fio api_fopen(struct api_file *self, struct lib9p_srv_ctx *ctx, bool, bool, bool) {
+	assert(self);
+	assert(ctx);
+	return lo_box_api_as_lib9p_srv_fio(self);
+}
+
+static void api_iofree(struct api_file *self) {
+	assert(self);
+}
+
+static uint32_t api_iounit(struct api_file *self) {
+	assert(self);
+	return 0;
+}
+
 static uint32_t api_pwrite(struct api_file *self, struct lib9p_srv_ctx *ctx, void *buf, uint32_t byte_count, uint64_t LM_UNUSED(offset)) {
 	assert(self);
 	assert(ctx);
@@ -111,7 +124,9 @@ static uint32_t api_pwrite(struct api_file *self, struct lib9p_srv_ctx *ctx, voi
 		LO_CALL(lo_box_hostnet_tcplist_as_net_stream_listener(&globals.listeners[i]), close);
 	return byte_count;
 }
-static uint32_t api_pread(struct api_file *, struct lib9p_srv_ctx *, void *, uint32_t, uint64_t) {
+static void api_pread(struct api_file *LM_UNUSED(self), struct lib9p_srv_ctx *LM_UNUSED(ctx),
+                      uint32_t LM_UNUSED(byte_count), uint64_t LM_UNUSED(byte_offset),
+                      struct iovec *LM_UNUSED(ret)) {
 	assert_notreached("not readable");
 }
 
diff --git a/lib9p_util/static.c b/lib9p_util/static.c
index a6ea8f6..7f1e6b7 100644
--- a/lib9p_util/static.c
+++ b/lib9p_util/static.c
@@ -12,6 +12,12 @@
 LO_IMPLEMENTATION_C(lib9p_srv_file, struct util9p_static_dir, util9p_static_dir, static);
 LO_IMPLEMENTATION_C(lib9p_srv_file, struct util9p_static_file, util9p_static_file, static);
 
+LO_IMPLEMENTATION_H(lib9p_srv_dio, struct util9p_static_dir, util9p_static_dir);
+LO_IMPLEMENTATION_C(lib9p_srv_dio, struct util9p_static_dir, util9p_static_dir, static);
+
+LO_IMPLEMENTATION_H(lib9p_srv_fio, struct util9p_static_file, util9p_static_file);
+LO_IMPLEMENTATION_C(lib9p_srv_fio, struct util9p_static_file, util9p_static_file, static);
+
 /* dir ************************************************************************/
 
 static void util9p_static_dir_free(struct util9p_static_dir *self) {
@@ -26,11 +32,6 @@ static struct lib9p_qid util9p_static_dir_qid(struct util9p_static_dir *self) {
 		.path = self->pathnum,
 	};
 }
-static uint32_t util9p_static_dir_chio(struct util9p_static_dir *self, struct lib9p_srv_ctx *ctx, bool, bool, bool) {
-	assert(self);
-	assert(ctx);
-	return 0;
-}
 
 static struct lib9p_stat util9p_static_dir_stat(struct util9p_static_dir *self, struct lib9p_srv_ctx *ctx) {
 	assert(self);
@@ -68,7 +69,7 @@ static void util9p_static_dir_remove(struct util9p_static_dir *self, struct lib9
 	lib9p_error(&ctx->basectx, LINUX_EROFS, "read-only part of filesystem");
 }
 
-static lo_interface lib9p_srv_file util9p_static_dir_dopen(struct util9p_static_dir *self, struct lib9p_srv_ctx *ctx,
+static lo_interface lib9p_srv_file util9p_static_dir_dwalk(struct util9p_static_dir *self, struct lib9p_srv_ctx *ctx,
                                                            struct lib9p_s childname) {
 	assert(self);
 	assert(ctx);
@@ -97,6 +98,16 @@ static lo_interface lib9p_srv_file util9p_static_dir_dcreate(struct util9p_stati
 	return LO_NULL(lib9p_srv_file);
 }
 
+LIB9P_SRV_NOTFILE(struct util9p_static_dir, util9p_static_dir);
+
+static lo_interface lib9p_srv_dio util9p_static_dir_dopen(struct util9p_static_dir *self, struct lib9p_srv_ctx *ctx) {
+	assert(self);
+	assert(ctx);
+	return lo_box_util9p_static_dir_as_lib9p_srv_dio(self);
+}
+static void util9p_static_dir_iofree(struct util9p_static_dir *self) {
+	assert(self);
+}
 static size_t util9p_static_dir_dread(struct util9p_static_dir *self, struct lib9p_srv_ctx *ctx,
                                       uint8_t *buf,
                                       uint32_t byte_count,
@@ -126,8 +137,6 @@ static size_t util9p_static_dir_dread(struct util9p_static_dir *self, struct lib
 	return obj_offset - _obj_offset;
 }
 
-LIB9P_SRV_NOTFILE(struct util9p_static_dir, util9p_static_dir)
-
 /* file ***********************************************************************/
 
 static void util9p_static_file_free(struct util9p_static_file *self) {
@@ -142,11 +151,6 @@ static struct lib9p_qid util9p_static_file_qid(struct util9p_static_file *self)
 		.path = self->pathnum,
 	};
 }
-static uint32_t util9p_static_file_chio(struct util9p_static_file *self, struct lib9p_srv_ctx *ctx, bool, bool, bool) {
-	assert(self);
-	assert(ctx);
-	return 0;
-}
 
 static inline size_t util9p_static_file_size(struct util9p_static_file *file) {
 	assert(file);
@@ -196,31 +200,46 @@ static void util9p_static_file_remove(struct util9p_static_file *self, struct li
 	lib9p_error(&ctx->basectx, LINUX_EROFS, "read-only part of filesystem");
 }
 
-LIB9P_SRV_NOTDIR(struct util9p_static_file, util9p_static_file)
+LIB9P_SRV_NOTDIR(struct util9p_static_file, util9p_static_file);
 
-static uint32_t util9p_static_file_pread(struct util9p_static_file *self, struct lib9p_srv_ctx *ctx,
-                                         void *buf,
-                                         uint32_t byte_count,
-                                         uint64_t byte_offset) {
+static lo_interface lib9p_srv_fio util9p_static_file_fopen(struct util9p_static_file *self, struct lib9p_srv_ctx *ctx,
+                                                           bool rd, bool wr, bool trunc) {
 	assert(self);
 	assert(ctx);
+	assert(rd);
+	assert(!wr);
+	assert(!trunc);
+	return lo_box_util9p_static_file_as_lib9p_srv_fio(self);
+}
+static void util9p_static_file_iofree(struct util9p_static_file *self) {
+	assert(self);
+}
+static uint32_t util9p_static_file_iounit(struct util9p_static_file *self) {
+	assert(self);
+	return 0;
+}
+static void util9p_static_file_pread(struct util9p_static_file *self, struct lib9p_srv_ctx *ctx,
+                                     uint32_t byte_count, uint64_t byte_offset,
+                                     struct iovec *ret) {
+	assert(self);
+	assert(ctx);
+	assert(ret);
 
 	size_t data_size = util9p_static_file_size(self);
 
 	if (byte_offset > (uint64_t)data_size) {
 		lib9p_error(&ctx->basectx,
 		            LINUX_EINVAL, "offset is past end-of-file length");
-		return 0;
+		return;
 	}
 
 	size_t beg_off = (size_t)byte_offset;
 	size_t end_off = beg_off + (size_t)byte_count;
 	if (end_off > data_size)
 		end_off = data_size;
-	memcpy(buf, &self->data_start[beg_off], end_off-beg_off);
-	return (uint32_t)(end_off-beg_off);
+	ret->iov_base = &self->data_start[beg_off];
+	ret->iov_len = end_off-beg_off;
 }
-
 static uint32_t util9p_static_file_pwrite(struct util9p_static_file *self, struct lib9p_srv_ctx *ctx,
                                           void *LM_UNUSED(buf),
                                           uint32_t LM_UNUSED(byte_count),
diff --git a/libcr_ipc/CMakeLists.txt b/libcr_ipc/CMakeLists.txt
index 4590bdd..3746584 100644
--- a/libcr_ipc/CMakeLists.txt
+++ b/libcr_ipc/CMakeLists.txt
@@ -21,9 +21,6 @@ set(ipc_tests
 	rpc
 	sema
 )
-if (ENABLE_TESTS)
-	foreach(test IN LISTS ipc_tests)
-		add_lib_test(libcr_ipc "test_${test}")
-		target_include_directories("test_${test}" PUBLIC ${CMAKE_CURRENT_SOURCE_DIR}/tests)
-	endforeach()
-endif()
+foreach(test IN LISTS ipc_tests)
+	add_lib_test(libcr_ipc "test_${test}")
+endforeach()
diff --git a/libhw/CMakeLists.txt b/libhw/CMakeLists.txt
deleted file mode 100644
index 242a3fa..0000000
--- a/libhw/CMakeLists.txt
+++ /dev/null
@@ -1,38 +0,0 @@
-# libhw/CMakeLists.txt - Device drivers
-#
-# Copyright (C) 2024-2025  Luke T. Shumaker <lukeshu@lukeshu.com>
-# SPDX-License-Identifier: AGPL-3.0-or-later
-
-add_library(libhw INTERFACE)
-target_link_libraries(libhw INTERFACE
-	libhw_generic
-)
-
-if (PICO_PLATFORM STREQUAL "rp2040")
-	target_include_directories(libhw SYSTEM INTERFACE ${CMAKE_CURRENT_SOURCE_DIR}/rp2040_include)
-	target_link_libraries(libhw INTERFACE
-		libcr_ipc
-	)
-	target_sources(libhw INTERFACE
-		rp2040_dma.c
-		rp2040_gpioirq.c
-		rp2040_hwspi.c
-		rp2040_hwtimer.c
-		w5500.c
-	)
-	target_link_libraries(libhw INTERFACE
-		hardware_gpio
-		hardware_irq
-		hardware_spi
-		hardware_timer
-	)
-endif()
-
-if (PICO_PLATFORM STREQUAL "host")
-	target_include_directories(libhw SYSTEM INTERFACE ${CMAKE_CURRENT_SOURCE_DIR}/host_include)
-	target_sources(libhw INTERFACE
-		host_util.c
-		host_alarmclock.c
-		host_net.c
-	)
-endif()
diff --git a/libhw_cr/CMakeLists.txt b/libhw_cr/CMakeLists.txt
new file mode 100644
index 0000000..caeac21
--- /dev/null
+++ b/libhw_cr/CMakeLists.txt
@@ -0,0 +1,43 @@
+# libhw_cr/CMakeLists.txt - Device drivers for libcr
+#
+# Copyright (C) 2024-2025  Luke T. Shumaker <lukeshu@lukeshu.com>
+# SPDX-License-Identifier: AGPL-3.0-or-later
+
+add_library(libhw_cr INTERFACE)
+target_link_libraries(libhw_cr INTERFACE
+	libhw_generic
+	libcr
+)
+
+target_sources(libhw_cr INTERFACE
+	alarmclock.c
+)
+
+if (PICO_PLATFORM STREQUAL "rp2040")
+	target_include_directories(libhw_cr SYSTEM INTERFACE ${CMAKE_CURRENT_SOURCE_DIR}/rp2040_include)
+	target_link_libraries(libhw_cr INTERFACE
+		libcr_ipc
+	)
+	target_sources(libhw_cr INTERFACE
+		rp2040_dma.c
+		rp2040_gpioirq.c
+		rp2040_hwspi.c
+		rp2040_hwtimer.c
+		w5500.c
+	)
+	target_link_libraries(libhw_cr INTERFACE
+		hardware_gpio
+		hardware_irq
+		hardware_spi
+		hardware_timer
+	)
+endif()
+
+if (PICO_PLATFORM STREQUAL "host")
+	target_include_directories(libhw_cr SYSTEM INTERFACE ${CMAKE_CURRENT_SOURCE_DIR}/host_include)
+	target_sources(libhw_cr INTERFACE
+		host_util.c
+		host_alarmclock.c
+		host_net.c
+	)
+endif()
diff --git a/libhw_cr/alarmclock.c b/libhw_cr/alarmclock.c
new file mode 100644
index 0000000..6eec52b
--- /dev/null
+++ b/libhw_cr/alarmclock.c
@@ -0,0 +1,23 @@
+/* libhw_cr/alarmclock.c - sleep() implementation for libcr
+ *
+ * Copyright (C) 2024-2025  Luke T. Shumaker <lukeshu@lukeshu.com>
+ * SPDX-License-Identifier: AGPL-3.0-or-later
+ */
+
+#include <libcr/coroutine.h>
+
+#include <libhw/generic/alarmclock.h>
+
+static void alarmclock_sleep_intrhandler(void *_arg) {
+	cid_t cid = *(cid_t *)_arg;
+	cr_unpause_from_intrhandler(cid);
+}
+
+void alarmclock_sleep_until_ns(lo_interface alarmclock clock, uint64_t abstime_ns) {
+	bool saved = cr_save_and_disable_interrupts();
+	cid_t cid = cr_getcid();
+	struct alarmclock_trigger trigger;
+	LO_CALL(clock, add_trigger, &trigger, abstime_ns, alarmclock_sleep_intrhandler, &cid);
+	cr_pause_and_yield();
+	cr_restore_interrupts(saved);
+}
diff --git a/libhw/host_alarmclock.c b/libhw_cr/host_alarmclock.c
index 19ece7c..2f255e0 100644
--- a/libhw/host_alarmclock.c
+++ b/libhw_cr/host_alarmclock.c
@@ -1,4 +1,4 @@
-/* libhw/host_alarmclock.c - <libhw/generic/alarmclock.h> implementation for POSIX hosts
+/* libhw_cr/host_alarmclock.c - <libhw/generic/alarmclock.h> implementation for POSIX hosts
  *
  * Copyright (C) 2024-2025  Luke T. Shumaker <lukeshu@lukeshu.com>
  * SPDX-License-Identifier: AGPL-3.0-or-later
diff --git a/libhw/host_include/libhw/host_alarmclock.h b/libhw_cr/host_include/libhw/host_alarmclock.h
index 89df68a..89df68a 100644
--- a/libhw/host_include/libhw/host_alarmclock.h
+++ b/libhw_cr/host_include/libhw/host_alarmclock.h
diff --git a/libhw/host_include/libhw/host_net.h b/libhw_cr/host_include/libhw/host_net.h
index fced229..fced229 100644
--- a/libhw/host_include/libhw/host_net.h
+++ b/libhw_cr/host_include/libhw/host_net.h
diff --git a/libhw/host_net.c b/libhw_cr/host_net.c
index e89cd66..f1c988c 100644
--- a/libhw/host_net.c
+++ b/libhw_cr/host_net.c
@@ -1,4 +1,4 @@
-/* libhw/host_net.c - <libhw/generic/net.h> implementation for hosted glibc
+/* libhw_cr/host_net.c - <libhw/generic/net.h> implementation for hosted glibc
  *
  * Copyright (C) 2024-2025  Luke T. Shumaker <lukeshu@lukeshu.com>
  * SPDX-License-Identifier: AGPL-3.0-or-later
diff --git a/libhw/host_util.c b/libhw_cr/host_util.c
index b862e39..958ed9c 100644
--- a/libhw/host_util.c
+++ b/libhw_cr/host_util.c
@@ -1,4 +1,4 @@
-/* libhw/host_util.c - Utilities for GNU/Linux hosts
+/* libhw_cr/host_util.c - Utilities for GNU/Linux hosts
  *
  * Copyright (C) 2024  Luke T. Shumaker <lukeshu@lukeshu.com>
  * SPDX-License-Identifier: AGPL-3.0-or-later
diff --git a/libhw/host_util.h b/libhw_cr/host_util.h
index f3ef6b4..8c53fab 100644
--- a/libhw/host_util.h
+++ b/libhw_cr/host_util.h
@@ -1,11 +1,11 @@
-/* libhw/host_util.h - Utilities for GNU/Linux hosts
+/* libhw_cr/host_util.h - Utilities for GNU/Linux hosts
  *
  * Copyright (C) 2024  Luke T. Shumaker <lukeshu@lukeshu.com>
  * SPDX-License-Identifier: AGPL-3.0-or-later
  */
 
-#ifndef _LIBHW_HOST_UTIL_H_
-#define _LIBHW_HOST_UTIL_H_
+#ifndef _LIBHW_CR_HOST_UTIL_H_
+#define _LIBHW_CR_HOST_UTIL_H_
 
 #include <time.h>                     /* for struct timespec */
 #include <sys/time.h>                 /* for struct timeval */
@@ -44,4 +44,4 @@ static inline uint64_t ns_from_host_ns_time(host_ns_time_t host_time) {
 		((uint64_t)host_time.tv_nsec);
 }
 
-#endif /* _LIBHW_HOST_UTIL_H_ */
+#endif /* _LIBHW_CR_HOST_UTIL_H_ */
diff --git a/libhw/rp2040_dma.c b/libhw_cr/rp2040_dma.c
index dfbf136..69116bf 100644
--- a/libhw/rp2040_dma.c
+++ b/libhw_cr/rp2040_dma.c
@@ -1,4 +1,4 @@
-/* libhw/rp2040_dma.c - Utilities for sharing the DMA IRQs
+/* libhw_cr/rp2040_dma.c - Utilities for sharing the DMA IRQs
  *
  * Copyright (C) 2025  Luke T. Shumaker <lukeshu@lukeshu.com>
  * SPDX-License-Identifier: AGPL-3.0-or-later
diff --git a/libhw/rp2040_dma.h b/libhw_cr/rp2040_dma.h
index c8d69b1..e295adf 100644
--- a/libhw/rp2040_dma.h
+++ b/libhw_cr/rp2040_dma.h
@@ -1,4 +1,4 @@
-/* libhw/rp2040_dma.h - Utilities for using DMA on the RP2040 (replaces <hardware/dma.h>)
+/* libhw_cr/rp2040_dma.h - Utilities for using DMA on the RP2040 (replaces <hardware/dma.h>)
  *
  * Copyright (c) 2020 Raspberry Pi (Trading) Ltd.
  * SPDX-License-Identifier: BSD-3-Clause
@@ -7,8 +7,8 @@
  * SPDX-License-Identifier: AGPL-3.0-or-later
  */
 
-#ifndef _LIBHW_RP2040_DMA_H_
-#define _LIBHW_RP2040_DMA_H_
+#ifndef _LIBHW_CR_RP2040_DMA_H_
+#define _LIBHW_CR_RP2040_DMA_H_
 
 #include <assert.h>
 #include <stdint.h> /* for uint32_t */
@@ -125,4 +125,4 @@ struct dma_alias3_short3                                  { READ_ADDR   ; };
 #define _DMA_TRIGGER_trans_count    struct dma_alias1
 #define _DMA_TRIGGER_ctrl           struct dma_alias0
 
-#endif /* _LIBHW_RP2040_DMA_H_ */
+#endif /* _LIBHW_CR_RP2040_DMA_H_ */
diff --git a/libhw/rp2040_gpioirq.c b/libhw_cr/rp2040_gpioirq.c
index 2f0ceac..1ae74f9 100644
--- a/libhw/rp2040_gpioirq.c
+++ b/libhw_cr/rp2040_gpioirq.c
@@ -1,4 +1,4 @@
-/* libhw/rp2040_gpioirq.c - Utilities for sharing the GPIO IRQ (IO_IRQ_BANK0)
+/* libhw_cr/rp2040_gpioirq.c - Utilities for sharing the GPIO IRQ (IO_IRQ_BANK0)
  *
  * Copyright (C) 2025  Luke T. Shumaker <lukeshu@lukeshu.com>
  * SPDX-License-Identifier: AGPL-3.0-or-later
diff --git a/libhw/rp2040_gpioirq.h b/libhw_cr/rp2040_gpioirq.h
index 06041c9..75a264f 100644
--- a/libhw/rp2040_gpioirq.h
+++ b/libhw_cr/rp2040_gpioirq.h
@@ -1,11 +1,11 @@
-/* libhw/rp2040_gpioirq.h - Utilities for sharing the GPIO IRQ (IO_IRQ_BANK0)
+/* libhw_cr/rp2040_gpioirq.h - Utilities for sharing the GPIO IRQ (IO_IRQ_BANK0)
  *
  * Copyright (C) 2025  Luke T. Shumaker <lukeshu@lukeshu.com>
  * SPDX-License-Identifier: AGPL-3.0-or-later
  */
 
-#ifndef _LIBHW_RP2040_GPIOIRQ_H_
-#define _LIBHW_RP2040_GPIOIRQ_H_
+#ifndef _LIBHW_CR_RP2040_GPIOIRQ_H_
+#define _LIBHW_CR_RP2040_GPIOIRQ_H_
 
 #include <hardware/gpio.h> /* for enum gpio_irq_level */
 
@@ -30,4 +30,4 @@ typedef void (*gpioirq_handler_t)(void *arg, uint gpio, enum gpio_irq_level even
  */
 void gpioirq_set_and_enable_exclusive_handler(uint gpio, enum gpio_irq_level event, gpioirq_handler_t fn, void *arg);
 
-#endif /* _LIBHW_RP2040_GPIOIRQ_H_ */
+#endif /* _LIBHW_CR_RP2040_GPIOIRQ_H_ */
diff --git a/libhw/rp2040_hwspi.c b/libhw_cr/rp2040_hwspi.c
index f747b1e..d4adb11 100644
--- a/libhw/rp2040_hwspi.c
+++ b/libhw_cr/rp2040_hwspi.c
@@ -1,4 +1,4 @@
-/* libhw/rp2040_hwspi.c - <libhw/generic/spi.h> implementation for the RP2040's ARM Primecell SSP (PL022)
+/* libhw_cr/rp2040_hwspi.c - <libhw/generic/spi.h> implementation for the RP2040's ARM Primecell SSP (PL022)
  *
  * Copyright (C) 2024-2025  Luke T. Shumaker <lukeshu@lukeshu.com>
  * SPDX-License-Identifier: AGPL-3.0-or-later
@@ -185,23 +185,23 @@ static void rp2040_hwspi_readwritev(struct rp2040_hwspi *self, const struct dupl
 		if (!iov[i].iov_len)
 			continue;
 		tx_data_blocks[j]    = (typeof(tx_data_blocks[0])){
-			.read_addr   = iov[i].iov_write_src ?: &self->bogus_data,
+			.read_addr   = (iov[i].iov_write_from != IOVEC_DISCARD) ? iov[i].iov_write_from : &self->bogus_data,
 			.write_addr  = &spi_get_hw(self->inst)->dr,
 			.trans_count = iov[i].iov_len,
 			.ctrl        = (DMA_CTRL_ENABLE
 			                | DMA_CTRL_DATA_SIZE(DMA_SIZE_8)
-			                | (iov[i].iov_write_src ? DMA_CTRL_INCR_READ : 0)
+			                | ((iov[i].iov_write_from != IOVEC_DISCARD) ? DMA_CTRL_INCR_READ : 0)
 			                | DMA_CTRL_CHAIN_TO(self->dma_tx_ctrl)
 			                | DMA_CTRL_TREQ_SEL(SPI_DREQ_NUM(self->inst, true))
 			                | DMA_CTRL_IRQ_QUIET),
 		};
 		rx_data_blocks[j]    = (typeof(rx_data_blocks[0])){
 			.read_addr   = &spi_get_hw(self->inst)->dr,
-			.write_addr  = iov[i].iov_read_dst ?: &bogus_rx_dst,
+			.write_addr  = (iov[i].iov_read_to != IOVEC_DISCARD) ? iov[i].iov_read_to : &bogus_rx_dst,
 			.trans_count = iov[i].iov_len,
 			.ctrl        = (DMA_CTRL_ENABLE
 			                | DMA_CTRL_DATA_SIZE(DMA_SIZE_8)
-			                | (iov[i].iov_read_dst ? DMA_CTRL_INCR_WRITE : 0)
+			                | ((iov[i].iov_read_to != IOVEC_DISCARD) ? DMA_CTRL_INCR_WRITE : 0)
 			                | DMA_CTRL_CHAIN_TO(self->dma_rx_ctrl)
 			                | DMA_CTRL_TREQ_SEL(SPI_DREQ_NUM(self->inst, false))
 			                | DMA_CTRL_IRQ_QUIET),
diff --git a/libhw/rp2040_hwtimer.c b/libhw_cr/rp2040_hwtimer.c
index ada6246..8227abb 100644
--- a/libhw/rp2040_hwtimer.c
+++ b/libhw_cr/rp2040_hwtimer.c
@@ -1,4 +1,4 @@
-/* libhw/rp2040_hwtimer.c - <libhw/generic/alarmclock.h> implementation for the RP2040's hardware timer
+/* libhw_cr/rp2040_hwtimer.c - <libhw/generic/alarmclock.h> implementation for the RP2040's hardware timer
  *
  * Copyright (C) 2024-2025  Luke T. Shumaker <lukeshu@lukeshu.com>
  * SPDX-License-Identifier: AGPL-3.0-or-later
diff --git a/libhw/rp2040_include/libhw/rp2040_hwspi.h b/libhw_cr/rp2040_include/libhw/rp2040_hwspi.h
index eb54cdc..9d99f7b 100644
--- a/libhw/rp2040_include/libhw/rp2040_hwspi.h
+++ b/libhw_cr/rp2040_include/libhw/rp2040_hwspi.h
@@ -48,7 +48,7 @@ LO_IMPLEMENTATION_H(spi, struct rp2040_hwspi, rp2040_hwspi)
  * @param mode        : enum spi_mode              : the SPI mode; SPI_MODE_{0..3}
  * @param baudrate_hz : uint                       : baudrate in Hz
  * @param min_delay_ns: uint64_t                   : minimum time for pin_cs to be high between messages
- * @param bogus_data  : uint8_t                    : bogus data to write when .iov_write_src is NULL
+ * @param bogus_data  : uint8_t                    : bogus data to write when .iov_write_from is IOVEC_DISCARD
  * @param pin_miso    : uint                       : pin number; 0, 4, 16, or 20 for _HWSPI_0; 8, 12, 24, or 28 for _HWSPI_1
  * @param pin_mosi    : uint                       : pin number; 3, 7, 19, or 23 for _HWSPI_0; 11, 15, or 27 for _HWSPI_1
  * @param pin_clk     : uint                       : pin number; 2, 6, 18, or 22 for _HWSPI_0; 10, 14, or 26 for _HWSPI_1
diff --git a/libhw/rp2040_include/libhw/rp2040_hwtimer.h b/libhw_cr/rp2040_include/libhw/rp2040_hwtimer.h
index 40e4172..40e4172 100644
--- a/libhw/rp2040_include/libhw/rp2040_hwtimer.h
+++ b/libhw_cr/rp2040_include/libhw/rp2040_hwtimer.h
diff --git a/libhw/rp2040_include/libhw/w5500.h b/libhw_cr/rp2040_include/libhw/w5500.h
index 51effba..51effba 100644
--- a/libhw/rp2040_include/libhw/w5500.h
+++ b/libhw_cr/rp2040_include/libhw/w5500.h
diff --git a/libhw/w5500.c b/libhw_cr/w5500.c
index c4d36f3..295add2 100644
--- a/libhw/w5500.c
+++ b/libhw_cr/w5500.c
@@ -1,4 +1,4 @@
-/* libhw/w5500.c - <libhw/generic/net.h> implementation for the WIZnet W5500 chip
+/* libhw_cr/w5500.c - <libhw/generic/net.h> implementation for the WIZnet W5500 chip
  *
  * Copyright (C) 2024-2025  Luke T. Shumaker <lukeshu@lukeshu.com>
  * SPDX-License-Identifier: AGPL-3.0-or-later
diff --git a/libhw/w5500_ll.h b/libhw_cr/w5500_ll.h
index 3822ad4..2506cd2 100644
--- a/libhw/w5500_ll.h
+++ b/libhw_cr/w5500_ll.h
@@ -1,4 +1,4 @@
-/* libhw/w5500_ll.h - Low-level header library for the WIZnet W5500 chip
+/* libhw_cr/w5500_ll.h - Low-level header library for the WIZnet W5500 chip
  *
  * Based entirely on the W5500 datasheet, v1.1.0.
  * https://docs.wiznet.io/img/products/w5500/W5500_ds_v110e.pdf
@@ -7,8 +7,8 @@
  * SPDX-License-Identifier: AGPL-3.0-or-later
  */
 
-#ifndef _LIBHW_W5500_LL_H_
-#define _LIBHW_W5500_LL_H_
+#ifndef _LIBHW_CR_W5500_LL_H_
+#define _LIBHW_CR_W5500_LL_H_
 
 #include <alloca.h> /* for alloca() */
 #include <stdint.h> /* for uint{n}_t */
@@ -93,39 +93,15 @@ w5500ll_writev(
 		(uint8_t)(addr & 0xFF),
 		(block & CTL_MASK_BLOCK) | CTL_W | CTL_OM_VDM,
 	};
-	struct duplex_iovec *inner = alloca(sizeof(struct duplex_iovec)*(iovcnt+1));
+	int inner_cnt = 1+io_slice_cnt(iov, iovcnt, skip, max);
+	struct duplex_iovec *inner = alloca(sizeof(struct duplex_iovec)*inner_cnt);
 	inner[0] = (struct duplex_iovec){
-		.iov_read_dst  = NULL,
-		.iov_write_src = header,
-		.iov_len       = sizeof(header),
+		.iov_read_to    = IOVEC_DISCARD,
+		.iov_write_from = header,
+		.iov_len        = sizeof(header),
 	};
-	int j = 1;
-	size_t skipped = 0, done = 0;
-	for (int i = 0; i < iovcnt && (max == 0 || done < max); i++) {
-		if (skipped < skip) {
-			if (skip - skipped >= iov[i].iov_len) {
-				skipped += iov[i].iov_len;
-				continue;
-			}
-			inner[j] = (struct duplex_iovec){
-				.iov_read_dst  = NULL,
-				.iov_write_src = iov[i].iov_base+(skip-skipped),
-				.iov_len       = iov[i].iov_len-(skip-skipped),
-			};
-			skipped = skip;
-		} else {
-			inner[j] = (struct duplex_iovec){
-				.iov_read_dst  = NULL,
-				.iov_write_src = iov[i].iov_base,
-				.iov_len       = iov[i].iov_len,
-			};
-		}
-		done += inner[j].iov_len;
-		if (max > 0 && done > max)
-			inner[j].iov_len -= done - max;
-		j++;
-	};
-	LO_CALL(spidev, readwritev, inner, j);
+	io_slice_wr_to_duplex(&inner[1], iov, iovcnt, skip, max);
+	LO_CALL(spidev, readwritev, inner, inner_cnt);
 }
 
 static inline void
@@ -154,26 +130,15 @@ w5500ll_readv(
 		(uint8_t)(addr & 0xFF),
 		(block & CTL_MASK_BLOCK) | CTL_R | CTL_OM_VDM,
 	};
-	struct duplex_iovec *inner = alloca(sizeof(struct duplex_iovec)*(iovcnt+1));
+	int inner_cnt = 1+io_slice_cnt(iov, iovcnt, 0, max);
+	struct duplex_iovec *inner = alloca(sizeof(struct duplex_iovec)*inner_cnt);
 	inner[0] = (struct duplex_iovec){
-		.iov_read_dst  = NULL,
-		.iov_write_src = header,
-		.iov_len       = sizeof(header),
-	};
-	int j = 1;
-	size_t done = 0;
-	for (int i = 0; i < iovcnt && (max == 0 || done < max); i++) {
-		inner[j] = (struct duplex_iovec){
-			.iov_read_dst  = iov[i].iov_base,
-			.iov_write_src = NULL,
-			.iov_len       = iov[i].iov_len,
-		};
-		done += inner[j].iov_len;
-		if (max > 0 && done > max)
-			inner[j].iov_len -= done - max;
-		j++;
+		.iov_read_to    = IOVEC_DISCARD,
+		.iov_write_from = header,
+		.iov_len        = sizeof(header),
 	};
-	LO_CALL(spidev, readwritev, inner, j);
+	io_slice_rd_to_duplex(&inner[1], iov, iovcnt, 0, max);
+	LO_CALL(spidev, readwritev, inner, inner_cnt);
 }
 
 /* Common chip-wide registers.  ***********************************************/
@@ -458,4 +423,4 @@ static_assert(sizeof(struct w5500ll_block_sock_reg) == 0x30);
 		val;                                                       \
 	})
 
-#endif /* _LIBHW_W5500_LL_H_ */
+#endif /* _LIBHW_CR_W5500_LL_H_ */
diff --git a/libhw_generic/CMakeLists.txt b/libhw_generic/CMakeLists.txt
index e38fbe9..5a6014b 100644
--- a/libhw_generic/CMakeLists.txt
+++ b/libhw_generic/CMakeLists.txt
@@ -8,10 +8,12 @@ target_include_directories(libhw_generic SYSTEM INTERFACE ${CMAKE_CURRENT_SOURCE
 target_link_libraries(libhw_generic INTERFACE
 	libmisc
 	libobj
-	libcr
 )
 
 target_sources(libhw_generic INTERFACE
 	alarmclock.c
+	io.c
 	net.c
 )
+
+add_lib_test(libhw_generic test_io)
diff --git a/libhw_generic/alarmclock.c b/libhw_generic/alarmclock.c
index 7fd049e..31fbbaf 100644
--- a/libhw_generic/alarmclock.c
+++ b/libhw_generic/alarmclock.c
@@ -1,25 +1,9 @@
-/* libhw_generic/alarmclock.c - Device-independent <libhw/generic/alarmclock.h> utilities
+/* libhw_generic/alarmclock.c - Device-independent <libhw/generic/alarmclock.h> storage
  *
  * Copyright (C) 2024-2025  Luke T. Shumaker <lukeshu@lukeshu.com>
  * SPDX-License-Identifier: AGPL-3.0-or-later
  */
 
-#include <libcr/coroutine.h>
-
 #include <libhw/generic/alarmclock.h>
 
 lo_interface alarmclock bootclock = {0};
-
-static void alarmclock_sleep_intrhandler(void *_arg) {
-	cid_t cid = *(cid_t *)_arg;
-	cr_unpause_from_intrhandler(cid);
-}
-
-void alarmclock_sleep_until_ns(lo_interface alarmclock clock, uint64_t abstime_ns) {
-	bool saved = cr_save_and_disable_interrupts();
-	cid_t cid = cr_getcid();
-	struct alarmclock_trigger trigger;
-	LO_CALL(clock, add_trigger, &trigger, abstime_ns, alarmclock_sleep_intrhandler, &cid);
-	cr_pause_and_yield();
-	cr_restore_interrupts(saved);
-}
diff --git a/libhw_generic/include/libhw/generic/io.h b/libhw_generic/include/libhw/generic/io.h
index a7f7378..7825c9f 100644
--- a/libhw_generic/include/libhw/generic/io.h
+++ b/libhw_generic/include/libhw/generic/io.h
@@ -8,6 +8,7 @@
 #define _LIBHW_GENERIC_IO_H_
 
 #include <stddef.h>    /* for size_t */
+#include <stdint.h>    /* for uintptr_t */
 #include <sys/types.h> /* for ssize_t */
 
 #include <libobj/obj.h>
@@ -23,12 +24,35 @@ struct iovec {
 };
 #endif
 
+#define IOVEC_DISCARD ((void*)(~((uintptr_t)0)))
+
 struct duplex_iovec {
-	void    *iov_read_dst;
-	void    *iov_write_src;
+	/**
+	 * NULL is a valid pointer value in iov_read_to and
+	 * iov_write_from.  To skip a read or write, use the special
+	 * value IOVEC_DISCARD.
+	 */
+	void    *iov_read_to;
+	void    *iov_write_from;
 	size_t   iov_len;
 };
 
+/* utilities ******************************************************************/
+
+/* slice iovec lists */
+int  io_slice_cnt       (                          const struct        iovec *src, int src_cnt, size_t byte_start, size_t byte_max_cnt);
+void io_slice           (struct        iovec *dst, const struct        iovec *src, int src_cnt, size_t byte_start, size_t byte_max_cnt);
+int  io_duplex_slice_cnt(                          const struct duplex_iovec *src, int src_cnt, size_t byte_start, size_t byte_max_cnt);
+void io_duplex_slice    (struct duplex_iovec *dst, const struct duplex_iovec *src, int src_cnt, size_t byte_start, size_t byte_max_cnt);
+
+/* convert iovec lists */
+void io_rd_to_duplex(struct duplex_iovec *dst, const struct iovec *src, int iovcnt);
+void io_wr_to_duplex(struct duplex_iovec *dst, const struct iovec *src, int iovcnt);
+
+/* slice and convert in one go */
+void io_slice_rd_to_duplex(struct duplex_iovec *dst, const struct iovec *src, int src_cnt, size_t byte_start, size_t byte_max_cnt);
+void io_slice_wr_to_duplex(struct duplex_iovec *dst, const struct iovec *src, int src_cnt, size_t byte_start, size_t byte_max_cnt);
+
 /* basic interfaces ***********************************************************/
 
 /**
diff --git a/libhw_generic/io.c b/libhw_generic/io.c
new file mode 100644
index 0000000..4ebff10
--- /dev/null
+++ b/libhw_generic/io.c
@@ -0,0 +1,98 @@
+/* libhw_generic/io.c - Utilities for device-independent I/O definitions
+ *
+ * Copyright (C) 2025  Luke T. Shumaker <lukeshu@lukeshu.com>
+ * SPDX-License-Identifier: AGPL-3.0-or-later
+ */
+
+#include <libmisc/assert.h>
+
+#include <libhw/generic/io.h>
+
+#define IOV_ITER(ACTION)                                                \
+	assert(src_cnt >= 0);                                           \
+	assert(src_cnt == 0 || src);                                    \
+                                                                        \
+	const size_t byte_end = byte_beg + byte_max_cnt;                \
+	int j = 0;                                                      \
+	size_t byte_pos = 0;                                            \
+	for (int i = 0;                                                 \
+	     i < src_cnt && (byte_max_cnt == 0 || byte_pos < byte_end); \
+	     i++) {                                                     \
+		size_t off = 0, len;                                    \
+		if (byte_pos < byte_beg) {                              \
+			if (byte_beg - byte_pos >= src[i].iov_len) {    \
+				byte_pos += src[i].iov_len;             \
+				continue;                               \
+			}                                               \
+			off = byte_beg-byte_pos;                        \
+			len = src[i].iov_len-off;                       \
+			byte_pos = byte_beg;                            \
+		} else {                                                \
+			len = src[i].iov_len;                           \
+		}                                                       \
+		if (byte_max_cnt && byte_end - byte_pos < len)          \
+			len = byte_end - byte_pos;                      \
+		do { ACTION } while (0);                                \
+		byte_pos += len;                                        \
+		j++;                                                    \
+	}
+
+int io_slice_cnt(const struct iovec *src, int src_cnt, size_t byte_beg, size_t byte_max_cnt) {
+	IOV_ITER();
+	return j;
+}
+
+int io_duplex_slice_cnt(const struct duplex_iovec *src, int src_cnt, size_t byte_beg, size_t byte_max_cnt) {
+	IOV_ITER();
+	return j;
+}
+
+void io_slice(struct iovec *dst, const struct iovec *src, int src_cnt, size_t byte_beg, size_t byte_max_cnt) {
+	assert(src_cnt == 0 || dst);
+	IOV_ITER(
+		dst[j] = ((struct iovec){
+			.iov_base = src[i].iov_base+off,
+			.iov_len  = len,
+		});
+	);
+}
+void io_slice_duplex(struct duplex_iovec *dst, const struct duplex_iovec *src, int src_cnt, size_t byte_beg, size_t byte_max_cnt) {
+	assert(src_cnt == 0 || dst);
+	IOV_ITER(
+		dst[j] = ((struct duplex_iovec){
+			.iov_read_to    = src[i].iov_read_to+off,
+			.iov_write_from = src[i].iov_write_from+off,
+			.iov_len        = len,
+		});
+	);
+}
+
+void io_slice_rd_to_duplex(struct duplex_iovec *dst, const struct iovec *src, int src_cnt, size_t byte_beg, size_t byte_max_cnt) {
+	assert(src_cnt == 0 || dst);
+	IOV_ITER(
+		dst[j] = ((struct duplex_iovec){
+			.iov_read_to    = src[i].iov_base+off,
+			.iov_write_from = IOVEC_DISCARD,
+			.iov_len        = len,
+		});
+	);
+}
+
+void io_slice_wr_to_duplex(struct duplex_iovec *dst, const struct iovec *src, int src_cnt, size_t byte_beg, size_t byte_max_cnt) {
+	assert(src_cnt == 0 || dst);
+	IOV_ITER(
+		dst[j] = ((struct duplex_iovec){
+			.iov_read_to    = IOVEC_DISCARD,
+			.iov_write_from = src[i].iov_base+off,
+			.iov_len        = len,
+		});
+	);
+}
+
+void io_rd_to_duplex(struct duplex_iovec *dst, const struct iovec *src, int iovcnt) {
+	io_slice_rd_to_duplex(dst, src, iovcnt, 0, 0);
+}
+
+void io_wr_to_duplex(struct duplex_iovec *dst, const struct iovec *src, int iovcnt) {
+	io_slice_wr_to_duplex(dst, src, iovcnt, 0, 0);
+}
diff --git a/libhw_generic/tests/test.h b/libhw_generic/tests/test.h
new file mode 120000
index 0000000..2fb1bd5
--- /dev/null
+++ b/libhw_generic/tests/test.h
@@ -0,0 +1 @@
+../../libmisc/tests/test.h
\ No newline at end of file
diff --git a/libhw_generic/tests/test_io.c b/libhw_generic/tests/test_io.c
new file mode 100644
index 0000000..0d6df11
--- /dev/null
+++ b/libhw_generic/tests/test_io.c
@@ -0,0 +1,57 @@
+/* libhw_generic/tests/test_io.c - Tests for <libmisc/io.h>
+ *
+ * Copyright (C) 2025  Luke T. Shumaker <lukeshu@lukeshu.com>
+ * SPDX-License-Identifier: AGPL-3.0-or-later
+ */
+
+#include <string.h>
+
+#include <libhw/generic/io.h>
+
+#include "test.h"
+
+int main() {
+	char data[] = "abcdefghijklmnopqrstuvwxyz";
+	struct iovec src[] = {
+		{.iov_base = &data[1], .iov_len=3}, /* "bcd" */
+		{.iov_base = &data[20], .iov_len=4}, /* "uvwx" */
+	};
+	const int src_cnt = sizeof(src)/sizeof(src[0]);
+
+	struct duplex_iovec dst[2];
+
+#define TC(start, max, ...) do {                                                                 \
+		char *exp[] = {__VA_ARGS__};                                                     \
+		int exp_cnt = sizeof(exp)/sizeof(exp[0]);                                        \
+		int act_cnt = io_slice_cnt(src, src_cnt, start, max);                            \
+		test_assert(act_cnt == exp_cnt);                                                 \
+		memset(dst, 0, sizeof(dst));                                                     \
+		io_slice_wr_to_duplex(dst, src, src_cnt, start, max);                            \
+		for (int i = 0; i < act_cnt; i++) {                                              \
+			test_assert(dst[i].iov_read_to == IOVEC_DISCARD);                        \
+			test_assert(dst[i].iov_write_from != IOVEC_DISCARD);                     \
+			test_assert(dst[i].iov_len == strlen(exp[i]));                           \
+			test_assert(memcmp(dst[i].iov_write_from, exp[i], dst[i].iov_len) == 0); \
+		}                                                                                \
+	} while (0)
+
+	TC(0, 0, /* => */ "bcd", "uvwx");
+	TC(1, 0, /* => */ "cd", "uvwx");
+	TC(2, 0, /* => */ "d", "uvwx");
+	TC(3, 0, /* => */ "uvwx");
+	TC(4, 0, /* => */ "vwx");
+	TC(5, 0, /* => */ "wx");
+	TC(6, 0, /* => */ "x");
+	TC(7, 0, /* => */ );
+
+	TC(0, 2, /* => */ "bc");
+	TC(1, 2, /* => */ "cd");
+	TC(2, 2, /* => */ "d", "u");
+	TC(3, 2, /* => */ "uv");
+	TC(4, 2, /* => */ "vw");
+	TC(5, 2, /* => */ "wx");
+	TC(6, 2, /* => */ "x");
+	TC(7, 2, /* => */ );
+
+	return 0;
+}