diff options
| -rw-r--r-- | block.c | 58 |
1 files changed, 48 insertions, 10 deletions
diff --git a/block.c b/block.c index 5d17aa1cc3..5ff6cbd796 100644 --- a/block.c +++ b/block.c @@ -2528,19 +2528,57 @@ static void bdrv_default_perms_for_storage(BlockDriverState *bs, BdrvChild *c, bdrv_filter_default_perms(bs, c, child_class, role, reopen_queue, perm, shared, &perm, &shared); - /* Format drivers may touch metadata even if the guest doesn't write */ - if (bdrv_is_writable_after_reopen(bs, reopen_queue)) { - perm |= BLK_PERM_WRITE | BLK_PERM_RESIZE; + if (role & BDRV_CHILD_METADATA) { + /* Format drivers may touch metadata even if the guest doesn't write */ + if (bdrv_is_writable_after_reopen(bs, reopen_queue)) { + perm |= BLK_PERM_WRITE | BLK_PERM_RESIZE; + } + + /* + * bs->file always needs to be consistent because of the + * metadata. We can never allow other users to resize or write + * to it. + */ + if (!(flags & BDRV_O_NO_IO)) { + perm |= BLK_PERM_CONSISTENT_READ; + } + shared &= ~(BLK_PERM_WRITE | BLK_PERM_RESIZE); } - /* - * bs->file always needs to be consistent because of the metadata. We - * can never allow other users to resize or write to it. - */ - if (!(flags & BDRV_O_NO_IO)) { - perm |= BLK_PERM_CONSISTENT_READ; + if (role & BDRV_CHILD_DATA) { + /* + * Technically, everything in this block is a subset of the + * BDRV_CHILD_METADATA path taken above, and so this could + * be an "else if" branch. However, that is not obvious, and + * this function is not performance critical, therefore we let + * this be an independent "if". + */ + + /* + * We cannot allow other users to resize the file because the + * format driver might have some assumptions about the size + * (e.g. because it is stored in metadata, or because the file + * is split into fixed-size data files). + */ + shared &= ~BLK_PERM_RESIZE; + + /* + * WRITE_UNCHANGED often cannot be performed as such on the + * data file. For example, the qcow2 driver may still need to + * write copied clusters on copy-on-read. + */ + if (perm & BLK_PERM_WRITE_UNCHANGED) { + perm |= BLK_PERM_WRITE; + } + + /* + * If the data file is written to, the format driver may + * expect to be able to resize it by writing beyond the EOF. + */ + if (perm & BLK_PERM_WRITE) { + perm |= BLK_PERM_RESIZE; + } } - shared &= ~(BLK_PERM_WRITE | BLK_PERM_RESIZE); if (bs->open_flags & BDRV_O_INACTIVE) { shared |= BLK_PERM_WRITE | BLK_PERM_RESIZE; |