Merge branch 'dk/use-nsec-runtime' into seen

The build-time knob 'USE_NSEC' for nanosecond stat precision has been
converted to a runtime configuration 'core.useNanosec', allowing
distributions to bundle one binary that adapts to filesystem
capabilities dynamically.

* dk/use-nsec-runtime:
  core: convert build-time USE_NSEC into runtime core.useNanosec
  environment: align repo_config_values_init with struct declaration
  meson: expose knob for xmlto relative links in manuals

Documentation/config/core.adoc

@@ -118,6 +118,13 @@ core.trustctime::
 	crawlers and some backup systems).
 	See linkgit:git-update-index[1]. True by default.
 
+core.useNanosec::
+	If true, use nanosecond precision for ctime and mtime
+	comparisions between the index and the working tree (if Git
+	was compiled to respect this option).
+	This is unsafe on some platforms;
+	see link:technical/racy-git.html[Racy Git]. False by default.
+
 core.splitIndex::
 	If true, the split-index feature of the index will be used.
 	See linkgit:git-update-index[1]. False by default.

Documentation/meson.build

@@ -379,13 +379,18 @@ foreach manpage, category : manpages
       output: fs.stem(manpage) + '.xml',
     )
 
+    man_base_url = 'file://' + htmldir + '/'
+    if get_option('man_base_url') != ''
+      man_base_url = get_option('man_base_url')
+    endif
+
     doc_targets += custom_target(
       command: [
         xmlto,
         '-m', '@INPUT0@',
         '-m', '@INPUT1@',
         '--stringparam',
-        'man.base.url.for.relative.links=' + get_option('prefix') / get_option('mandir'),
+        'man.base.url.for.relative.links=' + man_base_url,
         'man',
         manpage_xml_target,
         '-o',

Documentation/technical/racy-git.adoc

@@ -39,8 +39,8 @@ files) from `st_mode` member, `st_mtime` and `st_ctime`
 timestamps, `st_uid`, `st_gid`, `st_ino`, and `st_size` members.
 With a `USE_STDEV` compile-time option, `st_dev` is also
 compared, but this is not enabled by default because this member
-is not stable on network filesystems.  With `USE_NSEC`
+is not stable on network filesystems.  With 'core.useNanosec'
-compile-time option, `st_mtim.tv_nsec` and `st_ctim.tv_nsec`
+config setting, `st_mtim.tv_nsec` and `st_ctim.tv_nsec`
 members are also compared. On Linux, this is not enabled by default
 because in-core timestamps can have finer granularity than
 on-disk timestamps, resulting in meaningless changes when an
@@ -49,9 +49,10 @@ of git://git.kernel.org/pub/scm/linux/kernel/git/tglx/history.git
 ([PATCH] Sync in core time granularity with filesystems,
 2005-01-04). This patch is included in kernel 2.6.11 and newer, but
 only fixes the issue for file systems with exactly 1 ns or 1 s
-resolution. Other file systems are still broken in current Linux
+resolution.  As of kernel 4.3, other file systems (CEPH, CIFS, NTFS, UFS, FUSE)
-kernels (e.g. CEPH, CIFS, NTFS, UDF), see
+were fixed; see https://public-inbox.org/git/5605D88A.20104%40gmail.com/.  FAT
-https://lore.kernel.org/lkml/5577240D.7020309@gmail.com/
+has been fixed since 2015.  The usual suspects (ext2, ext4, XFS) are known to
+work, too.
 
 Racy Git
 --------

Makefile

@@ -202,18 +202,11 @@ include shared.mak
 # Define NO_NORETURN if using buggy versions of gcc 4.6+ and profile feedback,
 # as the compiler can crash (https://gcc.gnu.org/bugzilla/show_bug.cgi?id=49299)
 #
-# Define USE_NSEC below if you want git to care about sub-second file mtimes
-# and ctimes. Note that you need recent glibc (at least 2.2.4) for this. On
-# Linux, kernel 2.6.11 or newer is required for reliable sub-second file times
-# on file systems with exactly 1 ns or 1 s resolution. If you intend to use Git
-# on other file systems (e.g. CEPH, CIFS, NTFS, UDF), don't enable USE_NSEC. See
-# Documentation/technical/racy-git.adoc for details.
-#
 # Define USE_ST_TIMESPEC if your "struct stat" uses "st_ctimespec" instead of
 # "st_ctim"
 #
 # Define NO_NSEC if your "struct stat" does not have "st_ctim.tv_nsec"
-# available.  This automatically turns USE_NSEC off.
+# available.
 #
 # Define USE_STDEV below if you want git to care about the underlying device
 # change being considered an inode change from the update-index perspective.
@@ -1940,9 +1933,6 @@ endif
 ifdef NO_ST_BLOCKS_IN_STRUCT_STAT
 	BASIC_CFLAGS += -DNO_ST_BLOCKS_IN_STRUCT_STAT
 endif
-ifdef USE_NSEC
-	BASIC_CFLAGS += -DUSE_NSEC
-endif
 ifdef USE_ST_TIMESPEC
 	BASIC_CFLAGS += -DUSE_ST_TIMESPEC
 endif

builtin/update-index.c

@@ -130,7 +130,7 @@ static void xrmdir(const char *path)
 static void avoid_racy(void)
 {
 	/*
-	 * not use if we could usleep(10) if USE_NSEC is defined. The
+	 * not use if we could usleep(10) if core.useNanosec is enabled. The
 	 * field nsec could be there, but the OS could choose to
 	 * ignore it?
 	 */

compat/posix.h

@@ -518,7 +518,6 @@ int git_qsort_s(void *base, size_t nmemb, size_t size,
 } while (0)
 
 #ifdef NO_NSEC
-#undef USE_NSEC
 #define ST_ATIME_NSEC(st) 0
 #define ST_CTIME_NSEC(st) 0
 #define ST_MTIME_NSEC(st) 0

configure.ac

@@ -351,12 +351,6 @@ GIT_PARSE_WITH(iconv))
 
 ## --enable-FEATURE[=ARG] and --disable-FEATURE
 #
-# Define USE_NSEC below if you want git to care about sub-second file mtimes
-# and ctimes. Note that you need recent glibc (at least 2.2.4) for this, and
-# it will BREAK YOUR LOCAL DIFFS! show-diff and anything using it will likely
-# randomly break unless your underlying filesystem supports those sub-second
-# times (my ext3 doesn't).
-#
 # Define USE_STDEV below if you want git to care about the underlying device
 # change being considered an inode change from the update-index perspective.
 

environment.c

@@ -571,6 +571,13 @@ int git_default_core_config(const char *var, const char *value,
 		return 0;
 	}
 
+#ifndef NO_NSEC
+	if (!strcmp(var, "core.usenanosec")) {
+		cfg->use_nanosec = git_config_bool(var, value);
+		return 0;
+	}
+#endif
+
 	/* Add other config variables here and to Documentation/config.adoc. */
 	return platform_core_config(var, value, ctx, cb);
 }
@@ -745,6 +752,7 @@ int git_default_config(const char *var, const char *value,
 
 void repo_config_values_init(struct repo_config_values *cfg)
 {
+	/* section "core" config values */
 	cfg->attributes_file = NULL;
 	cfg->excludes_file = NULL;
 	cfg->editor_program = NULL;
@@ -756,20 +764,25 @@ void repo_config_values_init(struct repo_config_values *cfg)
 	cfg->autorebase = AUTOREBASE_NEVER;
 	cfg->object_creation_mode = OBJECT_CREATION_MODE;
 	cfg->apply_sparse_checkout = 0;
-	cfg->protect_hfs = PROTECT_HFS_DEFAULT;
-	cfg->protect_ntfs = PROTECT_NTFS_DEFAULT;
-	cfg->ignore_case = 0;
-	cfg->trust_executable_bit = 1;
-	cfg->has_symlinks = platform_has_symlinks();
-	cfg->branch_track = BRANCH_TRACK_REMOTE;
 	cfg->trust_ctime = 1;
 	cfg->check_stat = 1;
 	cfg->zlib_compression_level = Z_BEST_SPEED;
 	cfg->pack_compression_level = Z_DEFAULT_COMPRESSION;
 	cfg->precomposed_unicode = -1; /* see probe_utf8_pathname_composition() */
 	cfg->core_sparse_checkout_cone = 0;
-	cfg->sparse_expect_files_outside_of_patterns = 0;
 	cfg->warn_on_object_refname_ambiguity = 1;
+	cfg->protect_hfs = PROTECT_HFS_DEFAULT;
+	cfg->protect_ntfs = PROTECT_NTFS_DEFAULT;
+	cfg->ignore_case = 0;
+	cfg->trust_executable_bit = 1;
+	cfg->has_symlinks = platform_has_symlinks();
+	cfg->use_nanosec = 0;
+
+	/* section "sparse" config values */
+	cfg->sparse_expect_files_outside_of_patterns = 0;
+
+	/* section "branch" config values */
+	cfg->branch_track = BRANCH_TRACK_REMOTE;
 }
 
 void repo_config_values_clear(struct repo_config_values *cfg)

environment.h

@@ -138,6 +138,7 @@ struct repo_config_values {
 	int ignore_case;
 	int trust_executable_bit;
 	int has_symlinks;
+	int use_nanosec;
 	int sparse_expect_files_outside_of_patterns;
 	enum branch_track branch_track;
 };

meson_options.txt

@@ -115,6 +115,8 @@ option('default_help_format', type: 'combo', choices: ['man', 'html', 'platform'
   description: 'Default format used when executing git-help(1).')
 option('docs_backend', type: 'combo', choices: ['asciidoc', 'asciidoctor', 'auto'], value: 'auto',
   description: 'Which backend to use to generate documentation.')
+option('man_base_url', type: 'string', value: '',
+  description: 'The base URL to use for relative links in manuals')
 
 # Testing.
 option('benchmarks', type: 'feature', value: 'auto',

read-cache.c

@@ -354,15 +354,12 @@ static int is_racy_stat(const struct index_state *istate,
 			const struct stat_data *sd)
 {
 	return (istate->timestamp.sec &&
-#ifdef USE_NSEC
+		/* nanosecond timestamped files can also be racy! */
-		 /* nanosecond timestamped files can also be racy! */
+		(repo_config_values(istate->repo)->use_nanosec
-		(istate->timestamp.sec < sd->sd_mtime.sec ||
+		 ? (istate->timestamp.sec < sd->sd_mtime.sec ||
-		 (istate->timestamp.sec == sd->sd_mtime.sec &&
+		    (istate->timestamp.sec == sd->sd_mtime.sec &&
-		  istate->timestamp.nsec <= sd->sd_mtime.nsec))
+		     istate->timestamp.nsec <= sd->sd_mtime.nsec))
-#else
+		 : istate->timestamp.sec <= sd->sd_mtime.sec));
-		istate->timestamp.sec <= sd->sd_mtime.sec
-#endif
-		);
 }
 
 int is_racy_timestamp(const struct index_state *istate,

statinfo.c

@@ -72,13 +72,13 @@ int match_stat_data(const struct stat_data *sd, struct stat *st)
 	    sd->sd_ctime.sec != (unsigned int)st->st_ctime)
 		changed |= CTIME_CHANGED;
 
-#ifdef USE_NSEC
+	if (cfg->use_nanosec) {
-	if (cfg->check_stat && sd->sd_mtime.nsec != ST_MTIME_NSEC(*st))
+		if (cfg->check_stat && sd->sd_mtime.nsec != ST_MTIME_NSEC(*st))
-		changed |= MTIME_CHANGED;
+			changed |= MTIME_CHANGED;
-	if (cfg->trust_ctime && cfg->check_stat &&
+		if (cfg->trust_ctime && cfg->check_stat &&
-	    sd->sd_ctime.nsec != ST_CTIME_NSEC(*st))
+		    sd->sd_ctime.nsec != ST_CTIME_NSEC(*st))
-		changed |= CTIME_CHANGED;
+			changed |= CTIME_CHANGED;
-#endif
+	}
 
 	if (cfg->check_stat) {
 		if (sd->sd_uid != (unsigned int) st->st_uid ||