file-posix: Fix alignment after reopen changing O_DIRECT

At the end of a reopen, we already call bdrv_refresh_limits(), which
should update bs->request_alignment according to the new file
descriptor. However, raw_probe_alignment() relies on s->needs_alignment
and just uses 1 if it isn't set. We neglected to update this field, so
starting with cache=writeback and then reopening with cache=none means
that we get an incorrect bs->request_alignment == 1 and unaligned
requests fail instead of being automatically aligned.

Fix this by recalculating s->needs_alignment in raw_refresh_limits()
before calling raw_probe_alignment().

Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Message-Id: <20211104113109.56336-1-kwolf@redhat.com>
Reviewed-by: Hanna Reitz <hreitz@redhat.com>
Reviewed-by: Stefano Garzarella <sgarzare@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Message-Id: <20211115145409.176785-13-kwolf@redhat.com>
[hreitz: Fix iotest 142 for block sizes greater than 512 by operating on
         a file with a size of 1 MB]
Signed-off-by: Hanna Reitz <hreitz@redhat.com>
Message-Id: <20211116101431.105252-1-hreitz@redhat.com>

1 files changed, 16 insertions, 4 deletions

diff --git a/block/file-posix.c b/block/file-posix.c
index 7a27c83..b283093 100644
--- a/block/file-posix.c
+++ b/block/file-posix.c
@@ -167,6 +167,7 @@ typedef struct BDRVRawState {
     int page_cache_inconsistent; /* errno from fdatasync failure */
     bool has_fallocate;
     bool needs_alignment;
+    bool force_alignment;
     bool drop_cache;
     bool check_cache_dropped;
     struct {
@@ -351,6 +352,17 @@ static bool dio_byte_aligned(int fd)
     return false;
 }
 
+static bool raw_needs_alignment(BlockDriverState *bs)
+{
+    BDRVRawState *s = bs->opaque;
+
+    if ((bs->open_flags & BDRV_O_NOCACHE) != 0 && !dio_byte_aligned(s->fd)) {
+        return true;
+    }
+
+    return s->force_alignment;
+}
+
 /* Check if read is allowed with given memory buffer and length.
  *
  * This function is used to check O_DIRECT memory buffer and request alignment.
@@ -728,9 +740,6 @@ static int raw_open_common(BlockDriverState *bs, QDict *options,
 
     s->has_discard = true;
     s->has_write_zeroes = true;
-    if ((bs->open_flags & BDRV_O_NOCACHE) != 0 && !dio_byte_aligned(s->fd)) {
-        s->needs_alignment = true;
-    }
 
     if (fstat(s->fd, &st) < 0) {
         ret = -errno;
@@ -784,9 +793,10 @@ static int raw_open_common(BlockDriverState *bs, QDict *options,
          * so QEMU makes sure all IO operations on the device are aligned
          * to sector size, or else FreeBSD will reject them with EINVAL.
          */
-        s->needs_alignment = true;
+        s->force_alignment = true;
     }
 #endif
+    s->needs_alignment = raw_needs_alignment(bs);
 
 #ifdef CONFIG_XFS
     if (platform_test_xfs_fd(s->fd)) {
@@ -1251,7 +1261,9 @@ static void raw_refresh_limits(BlockDriverState *bs, Error **errp)
     BDRVRawState *s = bs->opaque;
     struct stat st;
 
+    s->needs_alignment = raw_needs_alignment(bs);
     raw_probe_alignment(bs, s->fd, errp);
+
     bs->bl.min_mem_alignment = s->buf_align;
     bs->bl.opt_mem_alignment = MAX(s->buf_align, qemu_real_host_page_size);