[Libguestfs] [nbdkit PATCH 3/4] blocksize-policy: Round extents to match minimum alignment

Since a client is very likely to make further I/O calls at offsets returned in a block status call (for example, 'nbdinfo --map --totals'), and the blocksize-policy filter can set a minimum alignment larger than what the plugin does by default, it makes sense to force extents to that alignment. Signed-off-by: Eric Blake <eblake(a)redhat.com&gt; --- tests/Makefile.am | 2 ++ filters/blocksize-policy/policy.c | 15 ++++++++++++++- 2 files changed, 16 insertions(+), 1 deletion(-) diff --git a/tests/Makefile.am b/tests/Makefile.am index 63730821..242a03e4 100644 --- a/tests/Makefile.am +++ b/tests/Makefile.am @@ -1656,11 +1656,13 @@ TESTS += \ test-blocksize-policy.sh \ test-blocksize-error-policy.sh \ test-blocksize-write-disconnect.sh \ + test-blocksize-policy-extents.sh \ $(NULL) EXTRA_DIST += \ test-blocksize-policy.sh \ test-blocksize-error-policy.sh \ test-blocksize-write-disconnect.sh \ + test-blocksize-policy-extents.sh \ $(NULL) if HAVE_BZLIB diff --git a/filters/blocksize-policy/policy.c b/filters/blocksize-policy/policy.c index 51bea91e..d656c956 100644 --- a/filters/blocksize-policy/policy.c +++ b/filters/blocksize-policy/policy.c @@ -38,6 +38,7 @@ #include <inttypes.h> #include <string.h> #include <errno.h> +#include <assert.h> #include <nbdkit-filter.h> @@ -373,10 +374,22 @@ policy_extents (nbdkit_next *next, void *handle, uint32_t count, uint64_t offset, uint32_t flags, struct nbdkit_extents *extents, int *err) { + uint32_t minimum, preferred, maximum; + int res; + if (check_policy (next, handle, "extents", false, count, offset, err) == -1) return -1; - return next->extents (next, count, offset, flags, extents, err); + /* Munge the plugin's response to values that match the alignment we + * are enforcing; that way, a client that performs later operations + * at boundaries determined by the block status result will still be + * aligned. Since check_policy succeeded, policy_block_size will too. + */ + res = policy_block_size (next, handle, + &minimum, &preferred, &maximum); + assert (res == 0); + return nbdkit_extents_aligned (next, count, offset, flags, + minimum ?: 1, extents, err); } static struct nbdkit_filter filter = { -- 2.49.0