From: Misono Tomohiro <misono.tomohiro@jp.fujitsu.com>

Date: Mon, 27 Jan 2020 19:02:15 +0000

Subject: [PATCH] virtiofsd: Fix data corruption with O_APPEND write in

 writeback mode

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When writeback mode is enabled (-o writeback), O_APPEND handling is

done in kernel. Therefore virtiofsd clears O_APPEND flag when open.

Otherwise O_APPEND flag takes precedence over pwrite() and write

data may corrupt.

Currently clearing O_APPEND flag is done in lo_open(), but we also

need the same operation in lo_create(). So, factor out the flag

update operation in lo_open() to update_open_flags() and call it

in both lo_open() and lo_create().

This fixes the failure of xfstest generic/069 in writeback mode

(which tests O_APPEND write data integrity).

Signed-off-by: Misono Tomohiro <misono.tomohiro@jp.fujitsu.com>

Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>

Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>

(cherry picked from commit 8e4e41e39eac5ee5f378d66f069a2f70a1734317)

---

 tools/virtiofsd/passthrough_ll.c | 66 ++++++++++++++++----------------

 1 file changed, 33 insertions(+), 33 deletions(-)

diff --git a/tools/virtiofsd/passthrough_ll.c b/tools/virtiofsd/passthrough_ll.c

index 948cb19c77..4c61ac5065 100644

--- a/tools/virtiofsd/passthrough_ll.c

+++ b/tools/virtiofsd/passthrough_ll.c

@@ -1692,6 +1692,37 @@ static void lo_releasedir(fuse_req_t req, fuse_ino_t ino,

     fuse_reply_err(req, 0);

 }

+static void update_open_flags(int writeback, struct fuse_file_info *fi)

+{

+    /*

+     * With writeback cache, kernel may send read requests even

+     * when userspace opened write-only

+     */

+    if (writeback && (fi->flags & O_ACCMODE) == O_WRONLY) {

+        fi->flags &= ~O_ACCMODE;

+        fi->flags |= O_RDWR;

+    }

+

+    /*

+     * With writeback cache, O_APPEND is handled by the kernel.

+     * This breaks atomicity (since the file may change in the

+     * underlying filesystem, so that the kernel's idea of the

+     * end of the file isn't accurate anymore). In this example,

+     * we just accept that. A more rigorous filesystem may want

+     * to return an error here

+     */

+    if (writeback && (fi->flags & O_APPEND)) {

+        fi->flags &= ~O_APPEND;

+    }

+

+    /*

+     * O_DIRECT in guest should not necessarily mean bypassing page

+     * cache on host as well. If somebody needs that behavior, it

+     * probably should be a configuration knob in daemon.

+     */

+    fi->flags &= ~O_DIRECT;

+}

+

 static void lo_create(fuse_req_t req, fuse_ino_t parent, const char *name,

                       mode_t mode, struct fuse_file_info *fi)

 {

@@ -1721,12 +1752,7 @@ static void lo_create(fuse_req_t req, fuse_ino_t parent, const char *name,

         goto out;

     }

-    /*

-     * O_DIRECT in guest should not necessarily mean bypassing page

-     * cache on host as well. If somebody needs that behavior, it

-     * probably should be a configuration knob in daemon.

-     */

-    fi->flags &= ~O_DIRECT;

+    update_open_flags(lo->writeback, fi);

     fd = openat(parent_inode->fd, name, (fi->flags | O_CREAT) & ~O_NOFOLLOW,

                 mode);

@@ -1936,33 +1962,7 @@ static void lo_open(fuse_req_t req, fuse_ino_t ino, struct fuse_file_info *fi)

     fuse_log(FUSE_LOG_DEBUG, "lo_open(ino=%" PRIu64 ", flags=%d)\n", ino,

              fi->flags);

-    /*

-     * With writeback cache, kernel may send read requests even

-     * when userspace opened write-only

-     */

-    if (lo->writeback && (fi->flags & O_ACCMODE) == O_WRONLY) {

-        fi->flags &= ~O_ACCMODE;

-        fi->flags |= O_RDWR;

-    }

-

-    /*

-     * With writeback cache, O_APPEND is handled by the kernel.

-     * This breaks atomicity (since the file may change in the

-     * underlying filesystem, so that the kernel's idea of the

-     * end of the file isn't accurate anymore). In this example,

-     * we just accept that. A more rigorous filesystem may want

-     * to return an error here

-     */

-    if (lo->writeback && (fi->flags & O_APPEND)) {

-        fi->flags &= ~O_APPEND;

-    }

-

-    /*

-     * O_DIRECT in guest should not necessarily mean bypassing page

-     * cache on host as well. If somebody needs that behavior, it

-     * probably should be a configuration knob in daemon.

-     */

-    fi->flags &= ~O_DIRECT;

+    update_open_flags(lo->writeback, fi);

     sprintf(buf, "%i", lo_fd(req, ino));

     fd = openat(lo->proc_self_fd, buf, fi->flags & ~O_NOFOLLOW);