libhw_generic: io.h: Define some new interfaces

1 files changed, 67 insertions, 2 deletions

diff --git a/libhw_generic/include/libhw/generic/io.h b/libhw_generic/include/libhw/generic/io.h
index 19edbe6..c615932 100644
--- a/libhw_generic/include/libhw/generic/io.h
+++ b/libhw_generic/include/libhw/generic/io.h
@@ -7,14 +7,21 @@
 #ifndef _LIBHW_GENERIC_IO_H_
 #define _LIBHW_GENERIC_IO_H_
 
-#include <stddef.h>    /* for size_t */
-#include <stdint.h>    /* for uintptr_t */
+#include <stddef.h> /* for size_t */
+#include <stdint.h> /* for uintptr_t, uint{n}_t, UINT{n}_MAX */
 
 #include <libmisc/error.h>
 #include <libmisc/obj.h>
 
 /* structs ********************************************************************/
 
+/* uoff_t ==========================================================*/
+
+typedef uint64_t uoff_t;
+#define UOFF_MAX UINT64_MAX
+DECLARE_ERROR_OR(uoff_t);
+DECLARE_ERROR_AND(uoff_t);
+
 /* iovec ===========================================================*/
 
 #if __unix__
@@ -71,6 +78,8 @@ void io_slice_wr_to_duplex(struct duplex_iovec *dst, const struct iovec *src, in
  * Conventions:
  *
  *  - Naming:
+ *     + The "p"[osition] prefix means an explicit `uoff_t offset`,
+ *       instead of using an internal cursor.
  *     + The "v"[ec] suffix means a sequence of iovecs, instead of a
  *       simple buf+len.
  *
@@ -95,6 +104,18 @@ LO_INTERFACE(io_reader);
 #define io_readv(r, iov, iovcnt) LO_CALL(r, readv, iov, iovcnt)
 #define io_read(r, buf, count) LO_CALL(r, readv, &((struct iovec){.iov_base = buf, .iov_len = count}), 1)
 
+/**
+ * Returns bytes-read on success.  A short read is *not* an error
+ * (unlike `write` methods).
+ *
+ * It is invalid to call preadv when the sum length of iovecs is 0.
+ */
+#define io_preader_LO_IFACE \
+	LO_FUNC(size_t_or_error, preadv, const struct iovec *iov, int iovcnt, uoff_t offset)
+LO_INTERFACE(io_preader);
+#define io_preadv(r, iov, iovcnt, off) LO_CALL(r, preadv, iov, iovcnt, off)
+#define io_pread(r, buf, count, off) LO_CALL(r, preadv, &((struct iovec){.iov_base = buf, .iov_len = count}), 1, off)
+
 /* write ===========================================================*/
 
 /**
@@ -112,6 +133,21 @@ LO_INTERFACE(io_writer);
 #define io_writev(w, iov, iovcnt) LO_CALL(w, writev, iov, iovcnt)
 #define io_write(w, buf, count) LO_CALL(w, writev, &((struct iovec){.iov_base = buf, .iov_len = count}), 1)
 
+/**
+ * Returns bytes-written.  A short write *is* an error (unlike `read`
+ * methods).
+ *
+ * Writes are *not* guaranteed to be atomic, so if you have concurrent
+ * writers then you should arrange for a mutex to protect the writer.
+ *
+ * It is invalid to call writev when the sum length of iovecs is 0.
+ */
+#define io_pwriter_LO_IFACE \
+	LO_FUNC(size_t_and_error, pwritev, const struct iovec *iov, int iovcnt, uoff_t offset)
+LO_INTERFACE(io_pwriter);
+#define io_pwritev(r, iov, iovcnt, off) LO_CALL(r, pwritev, iov, iovcnt, off)
+#define io_pwrite(r, buf, count, off) LO_CALL(r, pwritev, &((struct iovec){.iov_base = buf, .iov_len = count}), 1, off)
+
 /* readwrite =======================================================*/
 
 /**
@@ -130,6 +166,35 @@ LO_INTERFACE(io_duplex_readwriter);
 #define io_readwritev(rw, iov, iovcnt) \
 	LO_CALL(rw, readwritev, iov, iovcnt)
 
+/* read then write =================================================*/
+
+/**
+ * LO_CALL(src, pread_to, dst, src_offset, count) is functionally:
+ *
+ *     size_t_and_error copy(lo_interface io_writer dst, lo_interface io_preader src, uoff_t src_offset, size_t count) {
+ *         buf = malloc(count);
+ *         size_t_or_error read_r = io_pread(src, buf, count, src_offset);
+ *         if (read_r.is_err)
+ *             return ERROR_AND(size_t, 0, read_r.err);
+ *         size_t_and_error write_r = io_write(dst, buf, read_r.size_t);
+ *         free(buf);
+ *         return write_r;
+ *     }
+ *
+ * except that it does not need to allocate a buffer.  That is: It
+ * allows the reader to dump its data directly to the writer.  This
+ * allows us to save a copy when the reader already has an in-memory
+ * buffer containing the data.
+ *
+ * The above code defines when a short read/write is an error or not.
+ *
+ * It must call writev() exactly 0-or-1 times, and if it does call it,
+ * then it must be called with exactly 1 iovec.
+ */
+#define io_preader_to_LO_IFACE \
+	LO_FUNC(size_t_and_error, pread_to, lo_interface io_writer dst, uoff_t src_offset, size_t count)
+LO_INTERFACE(io_preader_to);
+
 /* close ===========================================================*/
 
 #define io_closer_LO_IFACE \