path: root/lib9p/srv.c

#include <assert.h>
#include <inttypes.h> /* for PRI* */
#include <stdio.h>    /* for fprintf(), stderr */
#include <string.h>   /* for strerror() */

#include <libcr/coroutine.h>
#include <libcr_ipc/chan.h>
#include <libcr_ipc/mutex.h>
#include <libnetio/netio.h>

#include <lib9p/srv.h>
#include "internal.h"

/* structs ********************************************************************/

#define NAME  fidmap
#define KEY_T uint32_t
#define VAL_T struct lib9p_srv_file
#define CAP   CONFIG_9P_MAX_FIDS
#include "map.h"

#define NAME  reqmap
#define KEY_T uint32_t
#define VAL_T struct lib9p_srv_reqctx
#define CAP   CONFIG_9P_MAX_REQS
#include "map.h"

/* The hierarchy of concepts is:
 *
 *     server -> connection -> session -> request
 *
 */

/* struct lib9p_srv {} is defined in <lib9p/srv.h> */

struct lib9p_conn {
	/* immutable */
	struct lib9p_srv        *parent_srv;
	int                      fd;
	cid_t                    reader; /* the lib9p_srv_read_cr() coroutine */
	/* mutable */
	cr_mutex_t               writelock;
};

struct lib9p_sess {
	/* immutable */
	struct lib9p_conn       *parent_conn;
	enum lib9p_version       version;
	uint32_t                 max_msg_size;
	uint32_t                 rerror_overhead;
	/* mutable */
	bool                     initialized;
	bool                     closing;
	struct reqmap            reqs;
	struct fidmap            fids;
};

struct lib9p_req {
	/* immutable */
	struct lib9p_sess       *parent_sess;
	uint16_t                 tag;
	/* mutable */
	uint8_t                 *net_bytes; /* CONFIG_9P_MAX_MSG_SIZE-sized */
	struct lib9p_ctx         ctx;
};

/* base utilities *************************************************************/

#define nonrespond_errorf(fmt, ...) fprintf(stderr, "error: " fmt "\n" __VA_OPT__(,) __VA_ARGS__)

static uint32_t rerror_overhead_for_version(enum lib9p_version version, uint8_t *scratch) {
	struct lib9p_ctx empty_ctx = {
		.version      = version,
		.max_msg_size = CONFIG_9P_MAX_MSG_SIZE,
	};
	struct lib9p_msg_Rerror empty_error = { 0 };

	assert(!lib9p_marshal(&empty_ctx, LIB9P_TYP_Rerror, 0, &empty_error, scratch));
	uint32_t min_msg_size = decode_u32le(scratch);
	assert(min_msg_size < (UINT32_MAX - UINT16_MAX));
	assert(CONFIG_9P_MAX_MSG_SIZE >= min_msg_size);

	return min_msg_size;
}

static void respond_error(struct lib9p_req *req) {
	assert(req->ctx.err_num);
	assert(req->ctx.err_msg[0]);

	ssize_t r;
	struct lib9p_msg_Rerror host = {
		.ename = {
			.len = strnlen(req->ctx.err_msg, CONFIG_9P_MAX_ERR_SIZE),
			.utf8 = req->ctx.err_msg,
		},
		.errno = req->ctx.err_num,
	};

	/* Truncate the error-string if necessary to avoid needing to return ERANGE.  */
	if (((uint32_t)host.ename.len) + req->parent_sess->rerror_overhead > req->parent_sess->max_msg_size)
		host.ename.len = req->parent_sess->max_msg_size - req->parent_sess->rerror_overhead;

	lib9p_marshal(&req->ctx, LIB9P_TYP_Rerror, req->tag, &host, req->net_bytes);

	cr_mutex_lock(&req->parent_sess->parent_conn->writelock);
	r = netio_write(req->parent_sess->parent_conn->fd, req->net_bytes, decode_u32le(req->net_bytes));
	cr_mutex_unlock(&req->parent_sess->parent_conn->writelock);
	if (r < 0)
		nonrespond_errorf("write: %s", strerror(-r));
}

/* read coroutine *************************************************************/

static bool read_at_least(int fd, uint8_t *buf, size_t goal, size_t *done) {
	assert(buf);
	assert(goal);
	assert(done);
	while (*done < goal) {
		ssize_t r = netio_read(fd, &buf[*done], CONFIG_9P_MAX_MSG_SIZE - *done);
		if (r < 0) {
			nonrespond_errorf("read: %s", strerror(-r));
			return true;
		} else if (r == 0) {
			if (*done != 0)
				nonrespond_errorf("read: unexpected EOF");
			return true;
		}
		*done += r;
	}
	return false;
}

static bool handle_Tmessage(struct lib9p_req *);

COROUTINE lib9p_srv_read_cr(void *_srv) {
	uint8_t buf[CONFIG_9P_MAX_MSG_SIZE];

	struct lib9p_srv *srv = _srv;
	assert(srv);
	cr_begin();

	uint32_t initial_rerror_overhead = rerror_overhead_for_version(0, buf);

	for (;;) {
		struct lib9p_conn conn = {
			.parent_srv = srv,
			.fd         = netio_accept(srv->sockfd),
			.reader     = cr_getcid(),
		};
		if (conn.fd < 0) {
			nonrespond_errorf("accept: %s", strerror(-conn.fd));
			continue;
		}

		struct lib9p_sess sess = {
			.parent_conn     = &conn,
			.version         = 0,
			.max_msg_size    = CONFIG_9P_MAX_MSG_SIZE,
			.rerror_overhead = initial_rerror_overhead,
			.initialized     = false,
		};
		for (;;) {
			/* Read the message.  */
			size_t done = 0;
			if (read_at_least(conn.fd, buf, 4, &done))
				goto close;
			size_t goal = decode_u32le(buf);
			if (goal < 7) {
				nonrespond_errorf("T-message is impossibly small");
				goto close;
			}
			if (read_at_least(conn.fd, buf, 7, &done))
				goto close;
			struct lib9p_req req = {
				.parent_sess = &sess,
				.tag         = decode_u16le(&buf[5]),
				.net_bytes   = buf,
				.ctx         = {
					.version      = sess.version,
					.max_msg_size = sess.max_msg_size,
				},
			};
			if (goal > sess.max_msg_size) {
				lib9p_errorf(&req.ctx, LINUX_EMSGSIZE, "T-message larger than %s limit (%zu > %"PRIu32")",
				             sess.initialized ? "negotiated" : "server", goal, sess.max_msg_size);
				respond_error(&req);
				continue;
			}
			if (read_at_least(conn.fd, buf, goal, &done))
				goto close;

			/* Handle the message... in another coroutine.  */
			_lib9p_srv_reqch_send_req(&srv->_reqch, &req);
		}
	close:
		netio_close(conn.fd, true, sess.reqs.len == 0);
		if (sess.reqs.len) {
			sess.closing = true;
			cr_pause_and_yield();
			assert(sess.reqs.len == 0);
			netio_close(conn.fd, false, true);
		}
	}

	cr_end();
}

/* write coroutine ************************************************************/

static void handle_Tversion(struct lib9p_req *ctx, struct lib9p_msg_Tversion *req, struct lib9p_msg_Rversion *resp);
static void handle_Tauth(struct lib9p_req *ctx, struct lib9p_msg_Tauth *req, struct lib9p_msg_Rauth *resp);
static void handle_Tattach(struct lib9p_req *ctx, struct lib9p_msg_Tattach *req, struct lib9p_msg_Rattach *resp);
static void handle_Tflush(struct lib9p_req *ctx, struct lib9p_msg_Tflush *req, struct lib9p_msg_Rflush *resp);
static void handle_Twalk(struct lib9p_req *ctx, struct lib9p_msg_Twalk *req, struct lib9p_msg_Rwalk *resp);
static void handle_Topen(struct lib9p_req *ctx, struct lib9p_msg_Topen *req, struct lib9p_msg_Ropen *resp);
static void handle_Tcreate(struct lib9p_req *ctx, struct lib9p_msg_Tcreate *req, struct lib9p_msg_Rcreate *resp);
static void handle_Tread(struct lib9p_req *ctx, struct lib9p_msg_Tread *req, struct lib9p_msg_Rread *resp);
static void handle_Twrite(struct lib9p_req *ctx, struct lib9p_msg_Twrite *req, struct lib9p_msg_Rwrite *resp);
static void handle_Tclunk(struct lib9p_req *ctx, struct lib9p_msg_Tclunk *req, struct lib9p_msg_Rclunk *resp);
static void handle_Tremove(struct lib9p_req *ctx, struct lib9p_msg_Tremove *req, struct lib9p_msg_Rremove *resp);
static void handle_Tstat(struct lib9p_req *ctx, struct lib9p_msg_Tstat *req, struct lib9p_msg_Rstat *resp);
static void handle_Twstat(struct lib9p_req *ctx, struct lib9p_msg_Twstat *req, struct lib9p_msg_Rwstat *resp);
static void handle_Tsession(struct lib9p_req *ctx, struct lib9p_msg_Tsession *req, struct lib9p_msg_Rsession *resp);
static void handle_Tsread(struct lib9p_req *ctx, struct lib9p_msg_Tsread *req, struct lib9p_msg_Rsread *resp);
static void handle_Tswrite(struct lib9p_req *ctx, struct lib9p_msg_Tswrite *req, struct lib9p_msg_Rswrite *resp);

COROUTINE lib9p_srv_write_cr(void *_srv) {
	uint8_t net[CONFIG_9P_MAX_MSG_SIZE];

	struct lib9p_srv *srv = _srv;
	assert(srv);
	cr_begin();

	for (;;) {
		/* Receive the request from the reader coroutine.  */
		struct lib9p_req req;
		_lib9p_srv_reqch_req_t req_handle;
		req_handle = _lib9p_srv_reqch_recv_req(&srv->_reqch);
		req = *req_handle.req;
		memcpy(net, req.net_bytes, decode_u32le(req.net_bytes));
		req.net_bytes = net;
		_lib9p_srv_reqch_send_resp(req_handle, 0); /* notify that we've copied req */

		handle_Tmessage(&req);

		reqmap_del(&req.parent_sess->reqs, req.tag);
		if (req.parent_sess->closing && !req.parent_sess->reqs.len)
			cr_unpause(req.parent_sess->parent_conn->reader);
	}

	cr_end();
}

static bool handle_Tmessage(struct lib9p_req *req) {
	uint8_t host_req[CONFIG_9P_MAX_HOSTMSG_SIZE];
	uint8_t host_resp[CONFIG_9P_MAX_HOSTMSG_SIZE];

	/* Unmarshal it.  */
	enum lib9p_msg_type typ = req->net_bytes[4];
	if (typ % 2 != 0) {
		lib9p_errorf(&req->ctx, LINUX_EOPNOTSUPP, "expected a T-message but got an R-message: message_type=%s",
		             lib9p_msg_type_str(typ));
		goto write;
	}
	ssize_t host_size = lib9p_validate(&req->ctx, req->net_bytes);
	if (host_size < 0)
		goto write;
	if ((size_t)host_size > sizeof(host_req)) {
		lib9p_errorf(&req->ctx, LINUX_EMSGSIZE, "unmarshalled payload larger than server limit (%zu > %zu)",
		             host_size, sizeof(host_req));
		goto write;
	}
	lib9p_unmarshal(&req->ctx, req->net_bytes, &typ, &req->tag, host_req);

	/* Handle it.  */
	switch (typ) {
	case LIB9P_TYP_Tversion:
		handle_Tversion(req, (struct lib9p_msg_Tversion *)host_req, (struct lib9p_msg_Rversion *)host_resp);
		break;
	case LIB9P_TYP_Tauth:
		handle_Tauth(req, (struct lib9p_msg_Tauth *)host_req, (struct lib9p_msg_Rauth *)host_resp);
		break;
	case LIB9P_TYP_Tattach:
		handle_Tattach(req, (struct lib9p_msg_Tattach *)host_req, (struct lib9p_msg_Rattach *)host_resp);
		break;
	case LIB9P_TYP_Tflush:
		handle_Tflush(req, (struct lib9p_msg_Tflush *)host_req, (struct lib9p_msg_Rflush *)host_resp);
		break;
	case LIB9P_TYP_Twalk:
		handle_Twalk(req, (struct lib9p_msg_Twalk *)host_req, (struct lib9p_msg_Rwalk *)host_resp);
		break;
	case LIB9P_TYP_Topen:
		handle_Topen(req, (struct lib9p_msg_Topen *)host_req, (struct lib9p_msg_Ropen *)host_resp);
		break;
	case LIB9P_TYP_Tcreate:
		handle_Tcreate(req, (struct lib9p_msg_Tcreate *)host_req, (struct lib9p_msg_Rcreate *)host_resp);
		break;
	case LIB9P_TYP_Tread:
		handle_Tread(req, (struct lib9p_msg_Tread *)host_req, (struct lib9p_msg_Rread *)host_resp);
		break;
	case LIB9P_TYP_Twrite:
		handle_Twrite(req, (struct lib9p_msg_Twrite *)host_req, (struct lib9p_msg_Rwrite *)host_resp);
		break;
	case LIB9P_TYP_Tclunk:
		handle_Tclunk(req, (struct lib9p_msg_Tclunk *)host_req, (struct lib9p_msg_Rclunk *)host_resp);
		break;
	case LIB9P_TYP_Tremove:
		handle_Tremove(req, (struct lib9p_msg_Tremove *)host_req, (struct lib9p_msg_Rremove *)host_resp);
		break;
	case LIB9P_TYP_Tstat:
		handle_Tstat(req, (struct lib9p_msg_Tstat *)host_req, (struct lib9p_msg_Rstat *)host_resp);
		break;
	case LIB9P_TYP_Twstat:
		handle_Twstat(req, (struct lib9p_msg_Twstat *)host_req, (struct lib9p_msg_Rwstat *)host_resp);
		break;
	case LIB9P_TYP_Tsession: /* 9P2000.e */
		handle_Tsession(req, (struct lib9p_msg_Tsession *)host_req, (struct lib9p_msg_Rsession *)host_resp);
		break;
	case LIB9P_TYP_Tsread: /* 9P2000.e */
		handle_Tsread(req, (struct lib9p_msg_Tsread *)host_req, (struct lib9p_msg_Rsread *)host_resp);
		break;
	case LIB9P_TYP_Tswrite: /* 9P2000.e */
		handle_Tswrite(req, (struct lib9p_msg_Tswrite *)host_req, (struct lib9p_msg_Rswrite *)host_resp);
		break;
	default:
		assert(false);
	}

 write:
	if (lib9p_ctx_has_error(&req->ctx)) {
		respond_error(req);
		return true;
	} else {
		if (lib9p_marshal(&req->ctx, typ+1, req->tag, host_resp, req->net_bytes))
			goto write;
		cr_mutex_lock(&req->parent_sess->parent_conn->writelock);
		netio_write(req->parent_sess->parent_conn->fd, req->net_bytes, decode_u32le(req->net_bytes));
		cr_mutex_unlock(&req->parent_sess->parent_conn->writelock);
		return false;
	}
}

static void handle_Tversion(struct lib9p_req *ctx, struct lib9p_msg_Tversion *req, struct lib9p_msg_Rversion *resp) {
	enum lib9p_version version = LIB9P_VER_unknown;

	if (req->version.len >= 6 &&
	    req->version.utf8[0] == '9' &&
	    req->version.utf8[1] == 'P' &&
	    '0' <= req->version.utf8[2] && req->version.utf8[2] <= '9' &&
	    '0' <= req->version.utf8[3] && req->version.utf8[3] <= '9' &&
	    '0' <= req->version.utf8[4] && req->version.utf8[4] <= '9' &&
	    '0' <= req->version.utf8[5] && req->version.utf8[5] <= '9' &&
	    (req->version.utf8[6] == '\0' || req->version.utf8[6] == '.')) {
		if (strcmp((char *)&req->version.utf8[6], ".u") == 0)
			version = LIB9P_VER_9P2000_u;
		else if (strcmp((char *)&req->version.utf8[6], ".e") == 0)
			version = LIB9P_VER_9P2000_e;
		else
			version = LIB9P_VER_9P2000;
	}

	uint32_t min_msg_size = rerror_overhead_for_version(version, ctx->net_bytes);
	if (req->max_msg_size < min_msg_size) {
		lib9p_errorf(&ctx->ctx, LINUX_EDOM, "requested max_msg_size is less than minimum for %s (%"PRIu32" < %"PRIu32")",
		             version, req->max_msg_size, min_msg_size);
		return;
	}

	struct lib9p_srv_reqctx subctx = {
		.base  = &ctx->ctx,
	};
	if (ctx->parent_sess->reqs.len) {
		ctx->parent_sess->closing = true;
		// TODO: send flush events
		cr_pause_and_yield();
		assert(ctx->parent_sess->reqs.len == 0);
	}
	if (ctx->parent_sess->fids.len) {
		uint32_t fid;
		struct lib9p_srv_file *fptr;
		MAP_FOREACH(&ctx->parent_sess->fids, fid, fptr) {
			fptr->vtable.free(&subctx, fptr->impldata);
			fidmap_del(&ctx->parent_sess->fids, fid);
		}
	}
	// TODO: replace session with a new one?

#pragma GCC diagnostic push
#pragma GCC diagnostic ignored "-Wdiscarded-qualifiers"
	resp->version.utf8 = lib9p_version_str(version);
#pragma GCC diagnostic pop
	resp->version.len = strlen((char *)resp->version.utf8);
	resp->max_msg_size = (CONFIG_9P_MAX_MSG_SIZE < req->max_msg_size)
		? CONFIG_9P_MAX_MSG_SIZE
		: req->max_msg_size;
}

static void handle_Tauth(struct lib9p_req *ctx, struct lib9p_msg_Tauth *req, struct lib9p_msg_Rauth *UNUSED(resp)) {
	if (!ctx->parent_sess->parent_conn->parent_srv->auth) {
		lib9p_error(&ctx->ctx, LINUX_EOPNOTSUPP, "authentication not required");
		return;
	}
	struct lib9p_srv_reqctx subctx = {
		.base  = &ctx->ctx,
		.uid   = req->n_uname,
		.uname = req->uname.utf8,
	};
	ctx->parent_sess->parent_conn->parent_srv->auth(&subctx, req->aname.utf8);
	lib9p_error(&ctx->ctx, LINUX_EOPNOTSUPP, "TODO: auth not implemented");
}

static void handle_Tattach(struct lib9p_req *ctx, struct lib9p_msg_Tattach *req, struct lib9p_msg_Rattach *resp) {
	struct lib9p_srv_reqctx subctx = {
		.base  = &ctx->ctx,
		.uid   = req->n_uname,
		.uname = req->uname.utf8,
	};
	if (ctx->parent_sess->parent_conn->parent_srv->auth) {
		/*
		struct lib9p_srv_filehandle *fh = fidmap_get(req->afid);
		if (!fh)
			lib9p_error(&ctx->ctx, LINUX_EACCES, "FID provided as auth-file is not a valid FID");
		else if (fh->type != FH_AUTH)
			lib9p_error(&ctx->ctx, LINUX_EACCES, "FID provided as auth-file is not an auth-file");
		else if (strcmp(fh->data.auth.uname, req->uname.utf8) != 0)
			lib9p_errorf(&ctx->ctx, LINUX_EACCES, "FID provided as auth-file is for user=\"%s\" and cannot be used for user=\"%s\"",
			             fh->data.auth.uname, req->uname.utf8);
		else if (strcmp(fh->data.auth.aname, req->aname.utf8) != 0)
			lib9p_errorf(&ctx->ctx, LINUX_EACCES, "FID provided as auth-file is for tree=\"%s\" and cannot be used for tree=\"%s\"",
			             fh->data.auth.aname, req->aname.utf8);
		else if (!fh->data.auth.authenticated)
			lib9p_error(&ctx->ctx, LINUX_EACCES, "FID provided as auth-file has not completed authentication");
		fh->refcount--;
		if (lib9p_ctx_has_error(&ctx->ctx))
			return;
		*/
		lib9p_error(&ctx->ctx, LINUX_EOPNOTSUPP, "TODO: auth not implemented");
		return;
	} else {
		if (req->afid != LIB9P_NOFID) {
			lib9p_error(&ctx->ctx, LINUX_EACCES, "FID provided as auth-file, but no auth-file is required");
			return;
		}
	}

	if (fidmap_load(&ctx->parent_sess->fids, req->fid)) {
		lib9p_error(&ctx->ctx, LINUX_EBADF, "FID already in use");
		return;
	}

	struct lib9p_srv_file rootdir = ctx->parent_sess->parent_conn->parent_srv->rootdir(&subctx, req->aname.utf8);
	if (lib9p_ctx_has_error(&ctx->ctx))
		return;

	struct lib9p_stat stat = rootdir.vtable.stat(&subctx, rootdir.impldata);
	if (lib9p_ctx_has_error(&ctx->ctx)) {
		if (rootdir.vtable.free)
			rootdir.vtable.free(&subctx, rootdir.impldata);
		return;
	}

	struct lib9p_srv_file *rootdir_ptr = fidmap_store(&ctx->parent_sess->fids, req->fid, rootdir);
	if (!rootdir_ptr) {
		lib9p_error(&ctx->ctx, LINUX_EMFILE, "too many open files");
		if (rootdir.vtable.free)
			rootdir.vtable.free(&subctx, rootdir.impldata);
		return;
	}

	resp->qid = stat.file_qid;
	return;
}

static void handle_Tflush(struct lib9p_req *ctx, struct lib9p_msg_Tflush *UNUSED(req), struct lib9p_msg_Rflush *UNUSED(resp)) {
	lib9p_error(&ctx->ctx, LINUX_EOPNOTSUPP, "flush not yet implemented");
}

static void handle_Twalk(struct lib9p_req *ctx, struct lib9p_msg_Twalk *UNUSED(req), struct lib9p_msg_Rwalk *UNUSED(resp)) {
	lib9p_error(&ctx->ctx, LINUX_EOPNOTSUPP, "walk not yet implemented");
}

static void handle_Topen(struct lib9p_req *ctx, struct lib9p_msg_Topen *UNUSED(req), struct lib9p_msg_Ropen *UNUSED(resp)) {
	lib9p_error(&ctx->ctx, LINUX_EOPNOTSUPP, "open not yet implemented");
}

static void handle_Tcreate(struct lib9p_req *ctx, struct lib9p_msg_Tcreate *UNUSED(req), struct lib9p_msg_Rcreate *UNUSED(resp)) {
	lib9p_error(&ctx->ctx, LINUX_EOPNOTSUPP, "create not yet implemented");
}

static void handle_Tread(struct lib9p_req *ctx, struct lib9p_msg_Tread *UNUSED(req), struct lib9p_msg_Rread *UNUSED(resp)) {
	lib9p_error(&ctx->ctx, LINUX_EOPNOTSUPP, "read not yet implemented");
}

static void handle_Twrite(struct lib9p_req *ctx, struct lib9p_msg_Twrite *UNUSED(req), struct lib9p_msg_Rwrite *UNUSED(resp)) {
	lib9p_error(&ctx->ctx, LINUX_EOPNOTSUPP, "write not yet implemented");
}

static void handle_Tclunk(struct lib9p_req *ctx, struct lib9p_msg_Tclunk *UNUSED(req), struct lib9p_msg_Rclunk *UNUSED(resp)) {
	lib9p_error(&ctx->ctx, LINUX_EOPNOTSUPP, "clunk not yet implemented");
}

static void handle_Tremove(struct lib9p_req *ctx, struct lib9p_msg_Tremove *UNUSED(req), struct lib9p_msg_Rremove *UNUSED(resp)) {
	lib9p_error(&ctx->ctx, LINUX_EOPNOTSUPP, "remove not yet implemented");
}

static void handle_Tstat(struct lib9p_req *ctx, struct lib9p_msg_Tstat *UNUSED(req), struct lib9p_msg_Rstat *UNUSED(resp)) {
	lib9p_error(&ctx->ctx, LINUX_EOPNOTSUPP, "stat not yet implemented");
}

static void handle_Twstat(struct lib9p_req *ctx, struct lib9p_msg_Twstat *UNUSED(req), struct lib9p_msg_Rwstat *UNUSED(resp)) {
	lib9p_error(&ctx->ctx, LINUX_EOPNOTSUPP, "wstat not yet implemented");
}

static void handle_Tsession(struct lib9p_req *ctx, struct lib9p_msg_Tsession *UNUSED(req), struct lib9p_msg_Rsession *UNUSED(resp)) {
	lib9p_error(&ctx->ctx, LINUX_EOPNOTSUPP, "session not yet implemented");
}

static void handle_Tsread(struct lib9p_req *ctx, struct lib9p_msg_Tsread *UNUSED(req), struct lib9p_msg_Rsread *UNUSED(resp)) {
	lib9p_error(&ctx->ctx, LINUX_EOPNOTSUPP, "sread not yet implemented");
}

static void handle_Tswrite(struct lib9p_req *ctx, struct lib9p_msg_Tswrite *UNUSED(req), struct lib9p_msg_Rswrite *UNUSED(resp)) {
	lib9p_error(&ctx->ctx, LINUX_EOPNOTSUPP, "swrite not yet implemented");
}