From 6b1a044afb363f03b51c9d0218bef44a34ea98c3 Mon Sep 17 00:00:00 2001 From: Kevin Wolf Date: Mon, 19 Dec 2016 15:21:48 +0100 Subject: [PATCH] block: Default .bdrv_child_perm() for format drivers Almost all format drivers have the same characteristics as far as permissions are concerned: They have one or more children for storing their own data and, more importantly, metadata (can be written to and grow even without external write requests, must be protected against other writers and present consistent data) and optionally a backing file (this is just data, so like for a filter, it only depends on what the parent nodes need). This provides a default implementation that can be shared by most of our format drivers. Signed-off-by: Kevin Wolf Acked-by: Fam Zheng Reviewed-by: Max Reitz --- block.c | 44 +++++++++++++++++++++++++++++++++++++++ include/block/block_int.h | 8 +++++++ 2 files changed, 52 insertions(+) diff --git a/block.c b/block.c index 064e9d77fa..d67819f2a2 100644 --- a/block.c +++ b/block.c @@ -1560,6 +1560,50 @@ void bdrv_filter_default_perms(BlockDriverState *bs, BdrvChild *c, (c->shared_perm & DEFAULT_PERM_UNCHANGED); } +void bdrv_format_default_perms(BlockDriverState *bs, BdrvChild *c, + const BdrvChildRole *role, + uint64_t perm, uint64_t shared, + uint64_t *nperm, uint64_t *nshared) +{ + bool backing = (role == &child_backing); + assert(role == &child_backing || role == &child_file); + + if (!backing) { + /* Apart from the modifications below, the same permissions are + * forwarded and left alone as for filters */ + bdrv_filter_default_perms(bs, c, role, perm, shared, &perm, &shared); + + /* Format drivers may touch metadata even if the guest doesn't write */ + if (!bdrv_is_read_only(bs)) { + 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. */ + perm |= BLK_PERM_CONSISTENT_READ; + shared &= ~(BLK_PERM_WRITE | BLK_PERM_RESIZE); + } else { + /* We want consistent read from backing files if the parent needs it. + * No other operations are performed on backing files. */ + perm &= BLK_PERM_CONSISTENT_READ; + + /* If the parent can deal with changing data, we're okay with a + * writable and resizable backing file. */ + /* TODO Require !(perm & BLK_PERM_CONSISTENT_READ), too? */ + if (shared & BLK_PERM_WRITE) { + shared = BLK_PERM_WRITE | BLK_PERM_RESIZE; + } else { + shared = 0; + } + + shared |= BLK_PERM_CONSISTENT_READ | BLK_PERM_GRAPH_MOD | + BLK_PERM_WRITE_UNCHANGED; + } + + *nperm = perm; + *nshared = shared; +} + static void bdrv_replace_child(BdrvChild *child, BlockDriverState *new_bs, bool check_new_perm) { diff --git a/include/block/block_int.h b/include/block/block_int.h index 17f4c2d6cd..eb0598e580 100644 --- a/include/block/block_int.h +++ b/include/block/block_int.h @@ -880,6 +880,14 @@ void bdrv_filter_default_perms(BlockDriverState *bs, BdrvChild *c, uint64_t perm, uint64_t shared, uint64_t *nperm, uint64_t *nshared); +/* Default implementation for BlockDriver.bdrv_child_perm() that can be used by + * (non-raw) image formats: Like above for bs->backing, but for bs->file it + * requires WRITE | RESIZE for read-write images, always requires + * CONSISTENT_READ and doesn't share WRITE. */ +void bdrv_format_default_perms(BlockDriverState *bs, BdrvChild *c, + const BdrvChildRole *role, + uint64_t perm, uint64_t shared, + uint64_t *nperm, uint64_t *nshared); const char *bdrv_get_parent_name(const BlockDriverState *bs); void blk_dev_change_media_cb(BlockBackend *blk, bool load); -- GitLab