file-posix: Fix crash on discard_granularity == 0

Block devices that don't support discard have a discard_granularity of
0. Currently, this results in a division by zero when we try to make
sure that it's a multiple of request_alignment. Only try to update
bs->bl.pdiscard_alignment when we got a non-zero discard_granularity
from sysfs.

Fixes: f605796aae4 ('file-posix: probe discard alignment on Linux block devices')
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Message-ID: <20250429155654.102735-1-kwolf@redhat.com>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>

diff --git a/block/file-posix.c b/block/file-posix.c
index 0d6e12f880ecd11ecb93bc3b17d655017bdd1522..0d85123d0fd886f73fbd244189ec87997634926c 100644 (file)
--- a/block/file-posix.c
+++ b/block/file-posix.c
@@ -1573,7 +1573,7 @@ static void raw_refresh_limits(BlockDriverState *bs, Error **errp)
         int ret;
 
         ret = hdev_get_pdiscard_alignment(&st, &dalign);
-        if (ret == 0) {
+        if (ret == 0 && dalign != 0) {
             uint32_t ralign = bs->bl.request_alignment;
 
             /* Probably never happens, but handle it just in case */