[PATCH 3/5] block: preserve errno from fdatasync failures

["Daniel P. Berrangé" <berrange@redhat.com>]

When fdatasync() fails on a file backend we set a flag that
short-circuits any future attempts to call fdatasync(). The
first failure returns the true errno, but the later short-
circuited calls return a generic EIO. The latter is unhelpful
because fdatasync() can return a variety of errnos, including
EACCESS.

Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>
---
 block/file-posix.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/block/file-posix.c b/block/file-posix.c
index 20e14f8e96..99cf452f84 100644
--- a/block/file-posix.c
+++ b/block/file-posix.c
@@ -160,7 +160,7 @@ typedef struct BDRVRawState {
     bool discard_zeroes:1;
     bool use_linux_aio:1;
     bool use_linux_io_uring:1;
-    bool page_cache_inconsistent:1;
+    int page_cache_inconsistent; /* errno from fdatasync failure */
     bool has_fallocate;
     bool needs_alignment;
     bool drop_cache;
@@ -1357,7 +1357,7 @@ static int handle_aiocb_flush(void *opaque)
     int ret;
 
     if (s->page_cache_inconsistent) {
-        return -EIO;
+        return -s->page_cache_inconsistent;
     }
 
     ret = qemu_fdatasync(aiocb->aio_fildes);
@@ -1376,7 +1376,7 @@ static int handle_aiocb_flush(void *opaque)
          * Obviously, this doesn't affect O_DIRECT, which bypasses the page
          * cache. */
         if ((s->open_flags & O_DIRECT) == 0) {
-            s->page_cache_inconsistent = true;
+            s->page_cache_inconsistent = errno;
         }
         return -errno;
     }
-- 
2.30.2