From f889054f031f2f01ae97bdc7579fbdf3a30e4e0e Mon Sep 17 00:00:00 2001 From: Max Reitz Date: Wed, 13 May 2020 13:05:28 +0200 Subject: [PATCH] block: Relax *perms_for_storage for data children We can be less restrictive about pure data children than those with metadata on them, so let bdrv_default_perms_for_storage() handle metadata children differently from pure data children. As explained in the code, the restrictions on metadata children are strictly stricter than those for pure data children, so in theory we just have to distinguish between pure-data and all other storage children (pure metadata or data+metadata). In practice, that is not obvious, though, so we have two independent code paths for metadata and for data children, and data+metadata children will go through both (without the path for data children doing anything meaningful). Signed-off-by: Max Reitz Message-Id: <20200513110544.176672-19-mreitz@redhat.com> Reviewed-by: Eric Blake Signed-off-by: Kevin Wolf --- block.c | 58 +++++++++++++++++++++++++++++++++++++++++++++++---------- 1 file 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;