block/io: skip head/tail requests on EINVAL

When guests send misaligned discard requests, the block layer breaks
them up into a misaligned head, an aligned main body, and a misaligned
tail.

The file-posix block driver on Linux returns -EINVAL on misaligned
discard requests. This causes bdrv_co_pdiscard() to fail and guests
configured with werror=stop will pause.

Add a special case for misaligned head/tail requests. Simply continue
when EINVAL is encountered so that the aligned main body of the request
can be completed and the guest is not paused. This is the best we can do
when guest discard limits do not match the host discard limits.

Fixes: https://issues.redhat.com/browse/RHEL-86032
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Reviewed-by: Hanna Czenczek <hreitz@redhat.com>
Message-ID: <20250417150528.76470-3-stefanha@redhat.com>
Reviewed-by: Kevin Wolf <kwolf@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>

1 files changed, 10 insertions, 5 deletions

diff --git a/block/io.c b/block/io.c
index 1ba8d1a..ccec113 100644
--- a/block/io.c
+++ b/block/io.c
@@ -3109,11 +3109,12 @@ int coroutine_fn bdrv_co_pdiscard(BdrvChild *child, int64_t offset,
     /* Invalidate the cached block-status data range if this discard overlaps */
     bdrv_bsc_invalidate_range(bs, offset, bytes);
 
-    /* Discard is advisory, but some devices track and coalesce
+    /*
+     * Discard is advisory, but some devices track and coalesce
      * unaligned requests, so we must pass everything down rather than
-     * round here.  Still, most devices will just silently ignore
-     * unaligned requests (by returning -ENOTSUP), so we must fragment
-     * the request accordingly.  */
+     * round here.  Still, most devices reject unaligned requests with
+     * -EINVAL or -ENOTSUP, so we must fragment the request accordingly.
+     */
     align = MAX(bs->bl.pdiscard_alignment, bs->bl.request_alignment);
     assert(align % bs->bl.request_alignment == 0);
     head = offset % align;
@@ -3180,7 +3181,11 @@ int coroutine_fn bdrv_co_pdiscard(BdrvChild *child, int64_t offset,
             }
         }
         if (ret && ret != -ENOTSUP) {
-            goto out;
+            if (ret == -EINVAL && (offset % align != 0 || num % align != 0)) {
+                /* Silently skip rejected unaligned head/tail requests */
+            } else {
+                goto out; /* bail out */
+            }
         }
 
         offset += num;