[PATCH 08/25] virtiofsd: Plumb fuse_bufvec through to do_write_buf

["Dr. David Alan Gilbert (git)" <dgilbert@redhat.com>]

From: "Dr. David Alan Gilbert" <dgilbert@redhat.com>

Let fuse_session_process_buf_int take a fuse_bufvec * instead of a
fuse_buf;  and then through to do_write_buf - where in the best
case it can pass that stragiht through to op.write_buf without copying
(other than ksipping a header).

Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
---
 contrib/virtiofsd/fuse_i.h        |  2 +-
 contrib/virtiofsd/fuse_lowlevel.c | 67 +++++++++++++++++++------------
 contrib/virtiofsd/fuse_virtio.c   |  3 +-
 3 files changed, 45 insertions(+), 27 deletions(-)

diff --git a/contrib/virtiofsd/fuse_i.h b/contrib/virtiofsd/fuse_i.h
index 4b718f1aec..06f3d88a44 100644
--- a/contrib/virtiofsd/fuse_i.h
+++ b/contrib/virtiofsd/fuse_i.h
@@ -119,7 +119,7 @@ int fuse_send_reply_iov_nofree(fuse_req_t req, int error, struct iovec *iov,
 void fuse_free_req(fuse_req_t req);
 
 void fuse_session_process_buf_int(struct fuse_session *se,
-				  const struct fuse_buf *buf, struct fuse_chan *ch);
+				  struct fuse_bufvec *bufv, struct fuse_chan *ch);
 
 
 #define FUSE_MAX_MAX_PAGES 256
diff --git a/contrib/virtiofsd/fuse_lowlevel.c b/contrib/virtiofsd/fuse_lowlevel.c
index dd046ecf07..2bd2ba00b9 100644
--- a/contrib/virtiofsd/fuse_lowlevel.c
+++ b/contrib/virtiofsd/fuse_lowlevel.c
@@ -1007,11 +1007,12 @@ static void do_write(fuse_req_t req, fuse_ino_t nodeid, const void *inarg)
 }
 
 static void do_write_buf(fuse_req_t req, fuse_ino_t nodeid, const void *inarg,
-			 const struct fuse_buf *ibuf)
+			 struct fuse_bufvec *ibufv)
 {
 	struct fuse_session *se = req->se;
-	struct fuse_bufvec bufv = {
-		.buf[0] = *ibuf,
+	struct fuse_bufvec *pbufv = ibufv;
+	struct fuse_bufvec tmpbufv = {
+		.buf[0] = ibufv->buf[0],
 		.count = 1,
 	};
 	struct fuse_write_in *arg = (struct fuse_write_in *) inarg;
@@ -1021,28 +1022,35 @@ static void do_write_buf(fuse_req_t req, fuse_ino_t nodeid, const void *inarg,
 	fi.fh = arg->fh;
 	fi.writepage = arg->write_flags & FUSE_WRITE_CACHE;
 
-	if (se->conn.proto_minor < 9) {
-		bufv.buf[0].mem = ((char *) arg) + FUSE_COMPAT_WRITE_IN_SIZE;
-		bufv.buf[0].size -= sizeof(struct fuse_in_header) +
-			FUSE_COMPAT_WRITE_IN_SIZE;
-		assert(!(bufv.buf[0].flags & FUSE_BUF_IS_FD));
-	} else {
-		fi.lock_owner = arg->lock_owner;
-		fi.flags = arg->flags;
-		if (!(bufv.buf[0].flags & FUSE_BUF_IS_FD))
-			bufv.buf[0].mem = PARAM(arg);
+	if (ibufv->count == 1) {
+		if (se->conn.proto_minor < 9) {
+			tmpbufv.buf[0].mem = ((char *) arg) + FUSE_COMPAT_WRITE_IN_SIZE;
+			tmpbufv.buf[0].size -= sizeof(struct fuse_in_header) +
+				FUSE_COMPAT_WRITE_IN_SIZE;
+			assert(!(tmpbufv.buf[0].flags & FUSE_BUF_IS_FD));
+		} else {
+			fi.lock_owner = arg->lock_owner;
+			fi.flags = arg->flags;
+			if (!(tmpbufv.buf[0].flags & FUSE_BUF_IS_FD))
+				tmpbufv.buf[0].mem = PARAM(arg);
 
-		bufv.buf[0].size -= sizeof(struct fuse_in_header) +
-			sizeof(struct fuse_write_in);
-	}
-	if (bufv.buf[0].size < arg->size) {
-		fuse_log(FUSE_LOG_ERR, "fuse: do_write_buf: buffer size too small\n");
-		fuse_reply_err(req, EIO);
-		return;
+			tmpbufv.buf[0].size -= sizeof(struct fuse_in_header) +
+				sizeof(struct fuse_write_in);
+		}
+		if (tmpbufv.buf[0].size < arg->size) {
+			fuse_log(FUSE_LOG_ERR, "fuse: do_write_buf: buffer size too small\n");
+			fuse_reply_err(req, EIO);
+			return;
+		}
+		tmpbufv.buf[0].size = arg->size;
+		pbufv = &tmpbufv;
+	} else {
+		// Input bufv contains the headers in the first element
+		// and the data in the rest, we need to skip that first element
+		ibufv->buf[0].size = 0;
 	}
-	bufv.buf[0].size = arg->size;
 
-	se->op.write_buf(req, nodeid, &bufv, arg->offset, &fi);
+	se->op.write_buf(req, nodeid, pbufv, arg->offset, &fi);
 }
 
 static void do_flush(fuse_req_t req, fuse_ino_t nodeid, const void *inarg)
@@ -1979,12 +1987,21 @@ static const char *opname(enum fuse_opcode opcode)
 void fuse_session_process_buf(struct fuse_session *se,
 			      const struct fuse_buf *buf)
 {
-	fuse_session_process_buf_int(se, buf, NULL);
+	struct fuse_bufvec bufv = { .buf[0] = *buf, .count = 1 };
+	fuse_session_process_buf_int(se, &bufv, NULL);
 }
 
+// Restriction:
+//   bufv is normally a single entry buffer, except for a write
+//   where (if it's in memory) then the bufv may be multiple entries,
+//   where the first entry contains all headers and subsequent entries
+//   contain data
+//   bufv shall not use any offsets etc to make the data anything
+//   other than contiguous starting from 0.
 void fuse_session_process_buf_int(struct fuse_session *se,
-				  const struct fuse_buf *buf, struct fuse_chan *ch)
+				  struct fuse_bufvec *bufv, struct fuse_chan *ch)
 {
+	const struct fuse_buf *buf = bufv->buf;
 	struct fuse_in_header *in;
 	const void *inarg;
 	struct fuse_req *req;
@@ -2057,7 +2074,7 @@ void fuse_session_process_buf_int(struct fuse_session *se,
 
 	inarg = (void *) &in[1];
 	if (in->opcode == FUSE_WRITE && se->op.write_buf)
-		do_write_buf(req, in->nodeid, inarg, buf);
+		do_write_buf(req, in->nodeid, inarg, bufv);
 	else
 		fuse_ll_ops[in->opcode].func(req, in->nodeid, inarg);
 
diff --git a/contrib/virtiofsd/fuse_virtio.c b/contrib/virtiofsd/fuse_virtio.c
index 1f09fad93d..68036e2171 100644
--- a/contrib/virtiofsd/fuse_virtio.c
+++ b/contrib/virtiofsd/fuse_virtio.c
@@ -499,7 +499,8 @@ static void *fv_queue_thread(void *opaque)
             /* TODO! Endianness of header */
 
             /* TODO: Add checks for fuse_session_exited */
-            fuse_session_process_buf_int(se, &fbuf, &ch);
+            struct fuse_bufvec bufv = { .buf[0] = fbuf, .count = 1 };
+            fuse_session_process_buf_int(se, &bufv, &ch);
 
             if (!qi->reply_sent) {
                 fuse_log(FUSE_LOG_DEBUG, "%s: elem %d no reply sent\n",
-- 
2.23.0