Gitweb: https://sourceware.org/git/?p=lvm2.git;a=commitdiff;h=4002f5e206ae89db28eb60... Commit: 4002f5e206ae89db28eb60bdfb3685bd926fed57 Parent: e932c5da50a22e585a3cd08edb3d849e7715e244 Author: Alasdair G Kergon agk@redhat.com AuthorDate: Tue Dec 12 18:36:54 2017 +0000 Committer: Alasdair G Kergon agk@redhat.com CommitterDate: Tue Dec 12 18:36:54 2017 +0000

format_text: Refactor and document metadata offset calculation.

--- lib/format_text/format-text.c | 47 +++++++++++++++++++++++++++------------- 1 files changed, 32 insertions(+), 15 deletions(-)

diff --git a/lib/format_text/format-text.c b/lib/format_text/format-text.c index 154d748..174a579 100644 --- a/lib/format_text/format-text.c +++ b/lib/format_text/format-text.c @@ -476,7 +476,9 @@ static struct raw_locn *_find_vg_rlocn(struct device_area *dev_area, }

/* - * Determine offset for uncommitted metadata + * Find first aligned offset after end of existing metadata. + * Based on the alignment provided, this is the exact offset to use for the new metadata. + * The caller is responsible for validating the result. */ static uint64_t _next_rlocn_offset(struct raw_locn *rlocn, struct mda_header *mdah, uint64_t mdac_area_start, uint64_t alignment) { @@ -484,7 +486,7 @@ static uint64_t _next_rlocn_offset(struct raw_locn *rlocn, struct mda_header *md

if (!rlocn) /* Find an empty slot */ - /* FIXME Assume only one VG per mdah for now */ + /* FIXME Assumes only one VG per mdah for now */ return alignment;

/* Calculate new start position relative to start of buffer rounded up to absolute alignment */ @@ -626,23 +628,28 @@ static int _metadata_fits_into_buffer(struct mda_context *mdac, struct mda_heade uint64_t old_wrap = 0; /* Amount of wrap around in existing metadata */ uint64_t new_end; /* The end location of the new metadata */

- /* Do we have existing metadata that ends beyond the end of the buffer? */ - if (rlocn && (rlocn->offset + rlocn->size > mdah->size)) - old_wrap = (rlocn->offset + rlocn->size) - mdah->size; + /* Does the total amount of metadata, old and new, fit inside the buffer? */ + if (MDA_HEADER_SIZE + (rlocn ? rlocn->size : 0) + mdac->rlocn.size >= mdah->size) + return_0;

- new_end = new_wrap ? new_wrap + MDA_HEADER_SIZE : - mdac->rlocn.offset + mdac->rlocn.size; + /* Does the existing metadata wrap around the end of the buffer? */ + if (rlocn) { + if (rlocn->offset + rlocn->size > mdah->size) + old_wrap = (rlocn->offset + rlocn->size) - mdah->size; + } + + new_end = new_wrap ? new_wrap + MDA_HEADER_SIZE : (mdac->rlocn.offset + mdac->rlocn.size);

/* If both wrap around, there's necessarily overlap */ if (new_wrap && old_wrap) return_0;

- /* If either wraps around, does the new end fall beyond the old start? */ - if (rlocn && (new_wrap || old_wrap) && (new_end > rlocn->offset)) - return_0; + /* If there's no existing metadata, we're OK */ + if (!rlocn) + return 1;

- /* Does the total amount of metadata, old and new, fit inside the buffer? */ - if (MDA_HEADER_SIZE + (rlocn ? rlocn->size : 0) + mdac->rlocn.size >= mdah->size) + /* If either wraps around, there's overlap if the new end falls beyond the old start */ + if ((new_wrap || old_wrap) && (new_end > rlocn->offset)) return_0;

return 1; @@ -658,6 +665,7 @@ static int _vg_write_raw(struct format_instance *fid, struct volume_group *vg, struct pv_list *pvl; int r = 0; uint64_t new_wrap; /* Number of bytes of new metadata that wrap around to start of buffer */ + uint64_t alignment = MDA_ORIGINAL_ALIGNMENT; int found = 0; int noprecommit = 0; const char *old_vg_name = NULL; @@ -675,6 +683,12 @@ static int _vg_write_raw(struct format_instance *fid, struct volume_group *vg, if (!found) return 1;

+ /* + * This is paired with the following closes: + * - at the end of this fn if returning 0 + * - in _vg_commit_raw_rlocn regardless of return code + * which handles commit (but not pre-commit) and revert. + */ if (!dev_open(mdac->area.dev)) return_0;

@@ -692,8 +706,10 @@ static int _vg_write_raw(struct format_instance *fid, struct volume_group *vg,

mdac->rlocn.size = fidtc->raw_metadata_buf_size;

- mdac->rlocn.offset = _next_rlocn_offset(rlocn, mdah, mdac->area.start, MDA_ORIGINAL_ALIGNMENT); + /* Find where the new metadata would be written with our preferred alignment */ + mdac->rlocn.offset = _next_rlocn_offset(rlocn, mdah, mdac->area.start, alignment);

+ /* Does the new metadata wrap around? */ if (mdac->rlocn.offset + mdac->rlocn.size > mdah->size) new_wrap = (mdac->rlocn.offset + mdac->rlocn.size) - mdah->size; else @@ -705,9 +721,9 @@ static int _vg_write_raw(struct format_instance *fid, struct volume_group *vg, goto out; }

- log_debug_metadata("Writing %s metadata to %s at " FMTu64 " len " FMTu64 " of " FMTu64, + log_debug_metadata("Writing %s metadata to %s at " FMTu64 " len " FMTu64 " of " FMTu64 " aligned to " FMTu64, vg->name, dev_name(mdac->area.dev), mdac->area.start + - mdac->rlocn.offset, mdac->rlocn.size - new_wrap, mdac->rlocn.size); + mdac->rlocn.offset, mdac->rlocn.size - new_wrap, mdac->rlocn.size, alignment);

/* Write text out, circularly */ if (!dev_write(mdac->area.dev, mdac->area.start + mdac->rlocn.offset, @@ -837,6 +853,7 @@ static int _vg_commit_raw_rlocn(struct format_instance *fid,

out: if (!precommit) { + /* This is an paired with the open at the start of _vg_write_raw */ if (!dev_close(mdac->area.dev)) stack;