[PATCH 3/9] read-cache.c: allow unaligned mapping of the index file
- From
Junio C Hamano <gitster@pobox.com>
- Date
- Apr 3, 2012, 22:53 UTC
- Message-ID
- <1333493596-14202-4-git-send-email-gitster@pobox.com>
- In-Reply-To
- <1333493596-14202-1-git-send-email-gitster@pobox.com>
Both the on-disk format v2 and v3 pads the "name" field to the multiple of eight to make sure that various quantities in network long/short type can be accessed with ntohl/ntohs without having to worry about alignment, but this forces us to waste disk I/O bandwidth.
Introduce ntoh_s()/ntoh_l() macros that the callers can use as if they were the regular ntohs()/ntohl() on a field that may not be aligned correctly.
Signed-off-by: Junio C Hamano <gitster@pobox.com> --- read-cache.c | 44 ++++++++++++++++++++++++++++++++------------ 1 file changed, 32 insertions(+), 12 deletions(-)
diff --git a/read-cache.c b/read-cache.c index fa8aa73..d8865f5 100644 --- a/read-cache.c +++ b/read-cache.c @@ -1285,6 +1285,26 @@ int read_index(struct index_state *istate) return read_index_from(istate, get_index_file()); } +#ifndef NEEDS_ALIGNED_ACCESS +#define ntoh_s(var) ntohs(var) +#define ntoh_l(var) ntohl(var) +#else +static inline uint16_t ntoh_s_force_align(void *p) +{ + uint16_t x; + memcpy(&x, p, sizeof(x)); + return ntohs(x); +} +static inline uint32_t ntoh_l_force_align(void *p) +{ + uint32_t x; + memcpy(&x, p, sizeof(x)); + return ntohl(x); +} +#define ntoh_s(var) ntoh_s_force_align(&(var)) +#define ntoh_l(var) ntoh_l_force_align(&(var)) +#endif + static struct cache_entry *create_from_disk(struct ondisk_cache_entry *ondisk) { struct cache_entry *ce; @@ -1293,14 +1313,14 @@ static struct cache_entry *create_from_disk(struct ondisk_cache_entry *ondisk) unsigned int flags; /* On-disk flags are just 16 bits */ - flags = ntohs(ondisk->flags); + flags = ntoh_s(ondisk->flags); len = flags & CE_NAMEMASK; if (flags & CE_EXTENDED) { struct ondisk_cache_entry_extended *ondisk2; int extended_flags; ondisk2 = (struct ondisk_cache_entry_extended *)ondisk; - extended_flags = ntohs(ondisk2->flags2) << 16; + extended_flags = ntoh_s(ondisk2->flags2) << 16; /* We do not yet understand any bit out of CE_EXTENDED_FLAGS */ if (extended_flags & ~CE_EXTENDED_FLAGS) die("Unknown index entry format %08x", extended_flags); @@ -1315,16 +1335,16 @@ static struct cache_entry *create_from_disk(struct ondisk_cache_entry *ondisk) ce = xmalloc(cache_entry_size(len)); - ce->ce_ctime.sec = ntohl(ondisk->ctime.sec); - ce->ce_mtime.sec = ntohl(ondisk->mtime.sec); - ce->ce_ctime.nsec = ntohl(ondisk->ctime.nsec); - ce->ce_mtime.nsec = ntohl(ondisk->mtime.nsec); - ce->ce_dev = ntohl(ondisk->dev); - ce->ce_ino = ntohl(ondisk->ino); - ce->ce_mode = ntohl(ondisk->mode); - ce->ce_uid = ntohl(ondisk->uid); - ce->ce_gid = ntohl(ondisk->gid); - ce->ce_size = ntohl(ondisk->size); + ce->ce_ctime.sec = ntoh_l(ondisk->ctime.sec); + ce->ce_mtime.sec = ntoh_l(ondisk->mtime.sec); + ce->ce_ctime.nsec = ntoh_l(ondisk->ctime.nsec); + ce->ce_mtime.nsec = ntoh_l(ondisk->mtime.nsec); + ce->ce_dev = ntoh_l(ondisk->dev); + ce->ce_ino = ntoh_l(ondisk->ino); + ce->ce_mode = ntoh_l(ondisk->mode); + ce->ce_uid = ntoh_l(ondisk->uid); + ce->ce_gid = ntoh_l(ondisk->gid); + ce->ce_size = ntoh_l(ondisk->size); ce->ce_flags = flags; hashcpy(ce->sha1, ondisk->sha1);
-- 1.7.10.rc4.54.g1d5dd3