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48a0dfc913
Racy Git problems persist today, manifesting themselves in the performance of commands like "git diff" in new worktrees [1]. We have long had a build knob "USE_NSEC" to tell Git to use in-core nanosecond precision when available, which mitigates most if not all racy issues, but most builds we know about it don't use it. In part, that's because someone distributing Git can't safely enable it at compile-time if they don't know exactly what platforms their distribution will be used on. [1]: https://lore.kernel.org/git/CALnO6CADMJSixqYvL1Yo8qKX5rWhKQ+2OoSEuPUh-yoeK9TseQ@mail.gmail.com These days, most platforms are likely to be safe for the USE_NSEC code. Regardless, we want to give users the ability to benefit from it. This requires exposing the compile-time gated code as a runtime option. In addition, update the Racy Git documentation and other mentions of USE_NSEC in the code. Best-viewed-with: --ignore-space-change Signed-off-by: D. Ben Knoble <ben.knoble@gmail.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>
135 lines
3.2 KiB
C
135 lines
3.2 KiB
C
#define USE_THE_REPOSITORY_VARIABLE
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#include "git-compat-util.h"
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#include "environment.h"
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#include "statinfo.h"
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#include "repository.h"
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/*
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* Munge st_size into an unsigned int.
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*/
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static unsigned int munge_st_size(off_t st_size) {
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unsigned int sd_size = st_size;
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/*
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* If the file is an exact multiple of 4 GiB, modify the value so it
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* doesn't get marked as racily clean (zero).
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*/
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if (!sd_size && st_size)
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return 0x80000000;
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else
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return sd_size;
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}
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void fill_stat_data(struct stat_data *sd, struct stat *st)
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{
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sd->sd_ctime.sec = (unsigned int)st->st_ctime;
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sd->sd_mtime.sec = (unsigned int)st->st_mtime;
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sd->sd_ctime.nsec = ST_CTIME_NSEC(*st);
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sd->sd_mtime.nsec = ST_MTIME_NSEC(*st);
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sd->sd_dev = st->st_dev;
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sd->sd_ino = st->st_ino;
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sd->sd_uid = st->st_uid;
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sd->sd_gid = st->st_gid;
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sd->sd_size = munge_st_size(st->st_size);
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}
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static void set_times(struct stat *st, const struct stat_data *sd)
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{
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st->st_ctime = sd->sd_ctime.sec;
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st->st_mtime = sd->sd_mtime.sec;
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#ifdef NO_NSEC
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; /* nothing */
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#else
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#ifdef USE_ST_TIMESPEC
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st->st_ctimespec.tv_nsec = sd->sd_ctime.nsec;
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st->st_mtimespec.tv_nsec = sd->sd_mtime.nsec;
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#else
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st->st_ctim.tv_nsec = sd->sd_ctime.nsec;
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st->st_mtim.tv_nsec = sd->sd_mtime.nsec;
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#endif
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#endif
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}
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void fake_lstat_data(const struct stat_data *sd, struct stat *st)
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{
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set_times(st, sd);
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st->st_dev = sd->sd_dev;
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st->st_ino = sd->sd_ino;
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st->st_uid = sd->sd_uid;
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st->st_gid = sd->sd_gid;
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st->st_size = sd->sd_size;
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}
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int match_stat_data(const struct stat_data *sd, struct stat *st)
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{
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int changed = 0;
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struct repo_config_values *cfg = repo_config_values(the_repository);
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if (sd->sd_mtime.sec != (unsigned int)st->st_mtime)
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changed |= MTIME_CHANGED;
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if (cfg->trust_ctime && cfg->check_stat &&
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sd->sd_ctime.sec != (unsigned int)st->st_ctime)
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changed |= CTIME_CHANGED;
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if (cfg->use_nanosec) {
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if (cfg->check_stat && sd->sd_mtime.nsec != ST_MTIME_NSEC(*st))
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changed |= MTIME_CHANGED;
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if (cfg->trust_ctime && cfg->check_stat &&
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sd->sd_ctime.nsec != ST_CTIME_NSEC(*st))
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changed |= CTIME_CHANGED;
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}
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if (cfg->check_stat) {
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if (sd->sd_uid != (unsigned int) st->st_uid ||
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sd->sd_gid != (unsigned int) st->st_gid)
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changed |= OWNER_CHANGED;
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if (sd->sd_ino != (unsigned int) st->st_ino)
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changed |= INODE_CHANGED;
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}
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#ifdef USE_STDEV
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/*
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* st_dev breaks on network filesystems where different
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* clients will have different views of what "device"
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* the filesystem is on
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*/
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if (cfg->check_stat && sd->sd_dev != (unsigned int) st->st_dev)
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changed |= INODE_CHANGED;
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#endif
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if (sd->sd_size != munge_st_size(st->st_size))
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changed |= DATA_CHANGED;
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return changed;
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}
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void stat_validity_clear(struct stat_validity *sv)
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{
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FREE_AND_NULL(sv->sd);
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}
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int stat_validity_check(struct stat_validity *sv, const char *path)
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{
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struct stat st;
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if (stat(path, &st) < 0)
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return sv->sd == NULL;
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if (!sv->sd)
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return 0;
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return S_ISREG(st.st_mode) && !match_stat_data(sv->sd, &st);
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}
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void stat_validity_update(struct stat_validity *sv, int fd)
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{
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struct stat st;
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if (fstat(fd, &st) < 0 || !S_ISREG(st.st_mode))
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stat_validity_clear(sv);
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else {
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if (!sv->sd)
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CALLOC_ARRAY(sv->sd, 1);
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fill_stat_data(sv->sd, &st);
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}
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}
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