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read-cache: read data in a hash-independent way

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Index entries are structured with a variety of fields up front, followed
by a hash and one or two flags fields.  Because the hash field is stored
in the middle of the structure, it's difficult to use one fixed-size
structure that easily allows access to the hash and flags fields.
Adjust the structure to hold the maximum amount of data that may be
needed using a member called "data" and read and write this field
independently in the various places that need to read and write the
structure.

Signed-off-by: brian m. carlson <sandals@crustytoothpaste.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
This commit is contained in:
brian m. carlson 2019-02-19 00:05:24 +00:00 committed by Junio C Hamano
parent 3899b88b49
commit 575fa8a3ed
1 changed files with 29 additions and 45 deletions
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74
read-cache.c
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@ -1640,39 +1640,24 @@ struct ondisk_cache_entry {
uint32_t uid;
uint32_t gid;
uint32_t size;
unsigned char sha1[20];
uint16_t flags;
char name[FLEX_ARRAY]; /* more */
};
/*
* This struct is used when CE_EXTENDED bit is 1
* The struct must match ondisk_cache_entry exactly from
* ctime till flags
*/
struct ondisk_cache_entry_extended {
struct cache_time ctime;
struct cache_time mtime;
uint32_t dev;
uint32_t ino;
uint32_t mode;
uint32_t uid;
uint32_t gid;
uint32_t size;
unsigned char sha1[20];
uint16_t flags;
uint16_t flags2;
char name[FLEX_ARRAY]; /* more */
/*
* unsigned char hash[hashsz];
* uint16_t flags;
* if (flags & CE_EXTENDED)
* uint16_t flags2;
*/
unsigned char data[GIT_MAX_RAWSZ + 2 * sizeof(uint16_t)];
char name[FLEX_ARRAY];
};
/* These are only used for v3 or lower */
#define align_padding_size(size, len) ((size + (len) + 8) & ~7) - (size + len)
#define align_flex_name(STRUCT,len) ((offsetof(struct STRUCT,name) + (len) + 8) & ~7)
#define align_flex_name(STRUCT,len) ((offsetof(struct STRUCT,data) + (len) + 8) & ~7)
#define ondisk_cache_entry_size(len) align_flex_name(ondisk_cache_entry,len)
#define ondisk_cache_entry_extended_size(len) align_flex_name(ondisk_cache_entry_extended,len)
#define ondisk_ce_size(ce) (((ce)->ce_flags & CE_EXTENDED) ? \
ondisk_cache_entry_extended_size(ce_namelen(ce)) : \
ondisk_cache_entry_size(ce_namelen(ce)))
#define ondisk_data_size(flags, len) (the_hash_algo->rawsz + \
((flags & CE_EXTENDED) ? 2 : 1) * sizeof(uint16_t) + len)
#define ondisk_data_size_max(len) (ondisk_data_size(CE_EXTENDED, len))
#define ondisk_ce_size(ce) (ondisk_cache_entry_size(ondisk_data_size((ce)->ce_flags, ce_namelen(ce))))
/* Allow fsck to force verification of the index checksum. */
int verify_index_checksum;
@ -1746,6 +1731,8 @@ static struct cache_entry *create_from_disk(struct mem_pool *ce_mem_pool,
struct cache_entry *ce;
size_t len;
const char *name;
const unsigned hashsz = the_hash_algo->rawsz;
const uint16_t *flagsp = (const uint16_t *)(ondisk->data + hashsz);
unsigned int flags;
size_t copy_len = 0;
/*
@ -1758,22 +1745,20 @@ static struct cache_entry *create_from_disk(struct mem_pool *ce_mem_pool,
int expand_name_field = version == 4;
/* On-disk flags are just 16 bits */
flags = get_be16(&ondisk->flags);
flags = get_be16(flagsp);
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 = get_be16(&ondisk2->flags2) << 16;
extended_flags = get_be16(flagsp + 1) << 16;
/* We do not yet understand any bit out of CE_EXTENDED_FLAGS */
if (extended_flags & ~CE_EXTENDED_FLAGS)
die(_("unknown index entry format 0x%08x"), extended_flags);
flags |= extended_flags;
name = ondisk2->name;
name = (const char *)(flagsp + 2);
}
else
name = ondisk->name;
name = (const char *)(flagsp + 1);
if (expand_name_field) {
const unsigned char *cp = (const unsigned char *)name;
@ -1812,7 +1797,9 @@ static struct cache_entry *create_from_disk(struct mem_pool *ce_mem_pool,
ce->ce_flags = flags & ~CE_NAMEMASK;
ce->ce_namelen = len;
ce->index = 0;
hashcpy(ce->oid.hash, ondisk->sha1);
hashcpy(ce->oid.hash, ondisk->data);
memcpy(ce->name, name, len);
ce->name[len] = '\0';
if (expand_name_field) {
if (copy_len)
@ -2556,6 +2543,8 @@ static void copy_cache_entry_to_ondisk(struct ondisk_cache_entry *ondisk,
struct cache_entry *ce)
{
short flags;
const unsigned hashsz = the_hash_algo->rawsz;
uint16_t *flagsp = (uint16_t *)(ondisk->data + hashsz);
ondisk->ctime.sec = htonl(ce->ce_stat_data.sd_ctime.sec);
ondisk->mtime.sec = htonl(ce->ce_stat_data.sd_mtime.sec);
@ -2567,15 +2556,13 @@ static void copy_cache_entry_to_ondisk(struct ondisk_cache_entry *ondisk,
ondisk->uid = htonl(ce->ce_stat_data.sd_uid);
ondisk->gid = htonl(ce->ce_stat_data.sd_gid);
ondisk->size = htonl(ce->ce_stat_data.sd_size);
hashcpy(ondisk->sha1, ce->oid.hash);
hashcpy(ondisk->data, ce->oid.hash);
flags = ce->ce_flags & ~CE_NAMEMASK;
flags |= (ce_namelen(ce) >= CE_NAMEMASK ? CE_NAMEMASK : ce_namelen(ce));
ondisk->flags = htons(flags);
flagsp[0] = htons(flags);
if (ce->ce_flags & CE_EXTENDED) {
struct ondisk_cache_entry_extended *ondisk2;
ondisk2 = (struct ondisk_cache_entry_extended *)ondisk;
ondisk2->flags2 = htons((ce->ce_flags & CE_EXTENDED_FLAGS) >> 16);
flagsp[1] = htons((ce->ce_flags & CE_EXTENDED_FLAGS) >> 16);
}
}
@ -2594,10 +2581,7 @@ static int ce_write_entry(git_hash_ctx *c, int fd, struct cache_entry *ce,
stripped_name = 1;
}
if (ce->ce_flags & CE_EXTENDED)
size = offsetof(struct ondisk_cache_entry_extended, name);
else
size = offsetof(struct ondisk_cache_entry, name);
size = offsetof(struct ondisk_cache_entry,data) + ondisk_data_size(ce->ce_flags, 0);
if (!previous_name) {
int len = ce_namelen(ce);
@ -2755,7 +2739,7 @@ static int do_write_index(struct index_state *istate, struct tempfile *tempfile,
struct cache_entry **cache = istate->cache;
int entries = istate->cache_nr;
struct stat st;
struct ondisk_cache_entry_extended ondisk;
struct ondisk_cache_entry ondisk;
struct strbuf previous_name_buf = STRBUF_INIT, *previous_name;
int drop_cache_tree = istate->drop_cache_tree;
off_t offset;