On 13.02.2017 18:22, Kevin Wolf wrote: > 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 <[email protected]> > --- > block.c | 37 +++++++++++++++++++++++++++++++++++++ > include/block/block_int.h | 8 ++++++++ > 2 files changed, 45 insertions(+) > > diff --git a/block.c b/block.c > index 290768d..8e99bb5 100644 > --- a/block.c > +++ b/block.c > @@ -1459,6 +1459,43 @@ 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 backing file. */
Are we OK with a resizable backing file, too? I'm not sure, actually.
Maybe we should just forbid it and hope nobody asks for it.
Max
> + shared &= BLK_PERM_WRITE;
> + 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)
> {
> diff --git a/include/block/block_int.h b/include/block/block_int.h
> index 2d74f92..46f51a6 100644
> --- a/include/block/block_int.h
> +++ b/include/block/block_int.h
> @@ -885,6 +885,14 @@ 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);
>
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