fuse_lowlevel: Set bufsize if HAVE_SPLICE is not define and avoid race

These are several buf size fixes

1) Set bufsize when HAVE_SPLICE is not defined. Addresses
https://github.com/libfuse/libfuse/issues/1184

2) Check in the read retry condition for bufsize, i.e. the value
passed to read and not for the buf->mem_size. Using buf->mem_size
can be startup racy. Additionally we now also set bufsize on
allocation to avoid these races.

3) Allocation and value assigned needs to follow the pattern

bufsize = se->bufsize;
buf_alloc(bufsize, internal)
buf->mem_size = bufsize;

I.e. bufsize has to be retrieved first, as se->bufsize might
change at anytime - the value used for allocation and
must not differ from the value actually used.

This also tries to set large sizes in passthrough_hp, to catch
issues in xfstests - though requires to set
/proc/sys/fs/fuse/max_pages_limit

Signed-off-by: Bernd Schubert <bschubert@ddn.com>

2 files changed, 13 insertions, 6 deletions

diff --git a/example/passthrough_hp.cc b/example/passthrough_hp.cc
index 41904e5..d87ca5f 100644
--- a/example/passthrough_hp.cc
+++ b/example/passthrough_hp.cc
@@ -226,6 +226,9 @@ static void sfs_init(void *userdata, fuse_conn_info *conn) {
 
     /* Disable the receiving and processing of FUSE_INTERRUPT requests */
     conn->no_interrupt = 1;
+
+    /* Try a large IO by default */
+    conn->max_write = 4 * 1024 * 1024;
 }
 
 
diff --git a/lib/fuse_lowlevel.c b/lib/fuse_lowlevel.c
index 17bc816..9ebaaf0 100644
--- a/lib/fuse_lowlevel.c
+++ b/lib/fuse_lowlevel.c
@@ -3112,16 +3112,16 @@ pipe_retry:
 		struct fuse_bufvec dst = { .count = 1 };
 
 		if (!buf->mem) {
-			buf->mem = buf_alloc(se->bufsize, internal);
+			buf->mem = buf_alloc(bufsize, internal);
 			if (!buf->mem) {
 				fuse_log(
 					FUSE_LOG_ERR,
 					"fuse: failed to allocate read buffer\n");
 				return -ENOMEM;
 			}
-			buf->mem_size = se->bufsize;
+			buf->mem_size = bufsize;
 		}
-		buf->size = se->bufsize;
+		buf->size = bufsize;
 		buf->flags = 0;
 		dst.buf[0] = *buf;
 
@@ -3151,14 +3151,18 @@ pipe_retry:
 
 fallback:
 #endif
+	bufsize = internal ? buf->mem_size : se->bufsize;
 	if (!buf->mem) {
-		buf->mem = buf_alloc(se->bufsize, internal);
+		bufsize = se->bufsize; /* might have changed */
+		buf->mem = buf_alloc(bufsize, internal);
 		if (!buf->mem) {
 			fuse_log(FUSE_LOG_ERR,
 				 "fuse: failed to allocate read buffer\n");
 			return -ENOMEM;
 		}
-		buf->mem_size = se->bufsize;
+
+		if (internal)
+			buf->mem_size = bufsize;
 	}
 
 restart:
@@ -3175,7 +3179,7 @@ restart:
 	if (fuse_session_exited(se))
 		return 0;
 	if (res == -1) {
-		if (err == EINVAL && internal && se->bufsize > buf->mem_size) {
+		if (err == EINVAL && internal && se->bufsize > bufsize) {
 			/* FUSE_INIT might have increased the required bufsize */
 			bufsize = se->bufsize;
 			void *newbuf = buf_alloc(bufsize, internal);