libblkid: add microsecond resolution for cache entries

The libblkid library uses stat.st_mtine to detect changes on the
device. The last update time of of the device in the cache is stored
as TIME= tag in the /etc/blkid.tab file.

Linux since 2.5.48 supports nanosecond resolution and more precise
time is available in the stat.st_mtim timespec struct.

This patch add microsecond precision to TIME= tag in the cache file,
old format:

	TIME="<sec>"

the new format:

	TIME="<sec>.<usec>"

This change is backwardly compatible.

Now, the blkid_verify() function checks stat.st_mtime and
stat.st_mtim.tv_nsec/1000.

Test:

 # e2label /dev/sdb1 AAAA

old version:

 # blkid -s LABEL /dev/sdb1; e2label /dev/sdb1 BBBB; blkid -s LABEL /dev/sdb1
 /dev/sdb1: LABEL="AAAA"
 /dev/sdb1: LABEL="AAAA"

new version:

 # blkid -s LABEL /dev/sdb1; e2label /dev/sdb1 BBBB; blkid -s LABEL /dev/sdb1
 /dev/sdb1: LABEL="AAAA"
 /dev/sdb1: LABEL="BBBB"

Signed-off-by: Karel Zak <kzak@redhat.com>

6 files changed, 51 insertions, 16 deletions

diff --git a/configure.ac b/configure.ac
index 9cc20b7a..96d7219f 100644
--- a/configure.ac
+++ b/configure.ac
@@ -601,6 +601,9 @@ AC_COMPILE_IFELSE([AC_LANG_PROGRAM([[
 AC_CHECK_MEMBERS([struct termios.c_line],,,
     [[#include <termios.h>]])
 
+AC_CHECK_MEMBERS([struct stat.st_mtim.tv_nsec],,,
+	[#include <sys/stat.h>])
+
 AC_CHECK_DECLS([
  ADDR_NO_RANDOMIZE,
  FDPIC_FUNCPTRS,
diff --git a/shlibs/blkid/src/blkidP.h b/shlibs/blkid/src/blkidP.h
index 1de6dd06..db5da5e8 100644
--- a/shlibs/blkid/src/blkidP.h
+++ b/shlibs/blkid/src/blkidP.h
@@ -19,6 +19,7 @@
 #include <sys/types.h>
 #include <dirent.h>
 #include <sys/stat.h>
+#include <sys/types.h>
 #include <stdio.h>
 #include <stdarg.h>
 #include <stdint.h>
@@ -45,6 +46,7 @@ struct blkid_struct_dev
 	int			bid_pri;	/* Device priority */
 	dev_t			bid_devno;	/* Device major/minor number */
 	time_t			bid_time;	/* Last update time of device */
+	suseconds_t		bid_utime;	/* Last update time (microseconds) */
 	unsigned int		bid_flags;	/* Device status bitflags */
 	char			*bid_label;	/* Shortcut to device LABEL */
 	char			*bid_uuid;	/* Shortcut to binary UUID */
diff --git a/shlibs/blkid/src/dev.c b/shlibs/blkid/src/dev.c
index e02f170c..24d989dd 100644
--- a/shlibs/blkid/src/dev.c
+++ b/shlibs/blkid/src/dev.c
@@ -84,7 +84,7 @@ void blkid_debug_dump_dev(blkid_dev dev)
 
 	printf("  dev: name = %s\n", dev->bid_name);
 	printf("  dev: DEVNO=\"0x%0llx\"\n", (long long)dev->bid_devno);
-	printf("  dev: TIME=\"%ld\"\n", (long)dev->bid_time);
+	printf("  dev: TIME=\"%ld.%ld\"\n", (long)dev->bid_time, (long)dev->bid_utime);
 	printf("  dev: PRI=\"%d\"\n", dev->bid_pri);
 	printf("  dev: flags = 0x%08X\n", dev->bid_flags);
 
diff --git a/shlibs/blkid/src/read.c b/shlibs/blkid/src/read.c
index b5e9cd02..e6aa0836 100644
--- a/shlibs/blkid/src/read.c
+++ b/shlibs/blkid/src/read.c
@@ -49,7 +49,8 @@ static void debug_dump_dev(blkid_dev dev);
  *
  *	The following tags are required for each entry:
  *	<ID="id">	unique (within this file) ID number of this device
- *	<TIME="time">	(ascii time_t) time this entry was last read from disk
+ *	<TIME="sec.usec"> (time_t and suseconds_t) time this entry was last
+ *	                 read from disk
  *	<TYPE="type">	(detected) type of filesystem/data for this partition
  *
  *	The following tags may be present, depending on the device contents
@@ -318,9 +319,12 @@ static int parse_tag(blkid_cache cache, blkid_dev dev, char **cp)
 		dev->bid_devno = STRTOULL(value, 0, 0);
 	else if (!strcmp(name, "PRI"))
 		dev->bid_pri = strtol(value, 0, 0);
-	else if (!strcmp(name, "TIME"))
-		dev->bid_time = STRTOULL(value, 0, 0);
-	else
+	else if (!strcmp(name, "TIME")) {
+		char *end = NULL;
+		dev->bid_time = STRTOULL(value, &end, 0);
+		if (end && *end == '.')
+			dev->bid_utime = STRTOULL(end + 1, 0, 0);
+	} else
 		ret = blkid_set_tag(dev, name, value, strlen(value));
 
 	DBG(DEBUG_READ, printf("    tag: %s=\"%s\"\n", name, value));
@@ -455,7 +459,7 @@ static void debug_dump_dev(blkid_dev dev)
 
 	printf("  dev: name = %s\n", dev->bid_name);
 	printf("  dev: DEVNO=\"0x%0llx\"\n", (long long)dev->bid_devno);
-	printf("  dev: TIME=\"%lld\"\n", (long long)dev->bid_time);
+	printf("  dev: TIME=\"%ld.%ld\"\n", (long)dev->bid_time, (long)dev->bid_utime);
 	printf("  dev: PRI=\"%d\"\n", dev->bid_pri);
 	printf("  dev: flags = 0x%08X\n", dev->bid_flags);
 
diff --git a/shlibs/blkid/src/save.c b/shlibs/blkid/src/save.c
index a1583ecc..c04c2242 100644
--- a/shlibs/blkid/src/save.c
+++ b/shlibs/blkid/src/save.c
@@ -37,9 +37,11 @@ static int save_dev(blkid_dev dev, FILE *file)
 	    printf("device %s, type %s\n", dev->bid_name, dev->bid_type ?
 		   dev->bid_type : "(null)"));
 
-	fprintf(file,
-		"<device DEVNO=\"0x%04lx\" TIME=\"%ld\"",
-		(unsigned long) dev->bid_devno, (long) dev->bid_time);
+	fprintf(file, "<device DEVNO=\"0x%04lx\" TIME=\"%ld.%ld\"",
+			(unsigned long) dev->bid_devno,
+			(long) dev->bid_time,
+			(long) dev->bid_utime);
+
 	if (dev->bid_pri)
 		fprintf(file, " PRI=\"%d\"", dev->bid_pri);
 	list_for_each(p, &dev->bid_tags) {
diff --git a/shlibs/blkid/src/verify.c b/shlibs/blkid/src/verify.c
index 27360260..a0cb3fea 100644
--- a/shlibs/blkid/src/verify.c
+++ b/shlibs/blkid/src/verify.c
@@ -11,6 +11,7 @@
 #include <unistd.h>
 #include <fcntl.h>
 #include <time.h>
+#include <sys/time.h>
 #include <sys/types.h>
 #ifdef HAVE_SYS_STAT_H
 #include <sys/stat.h>
@@ -73,19 +74,34 @@ blkid_dev blkid_verify(blkid_cache cache, blkid_dev dev)
 		return NULL;
 	}
 
-	if ((now >= dev->bid_time) &&
-	    (st.st_mtime <= dev->bid_time) &&
-	    ((diff < BLKID_PROBE_MIN) ||
-	     (dev->bid_flags & BLKID_BID_FL_VERIFIED &&
-	      diff < BLKID_PROBE_INTERVAL)))
+	if (now >= dev->bid_time &&
+#ifdef HAVE_STRUCT_STAT_ST_MTIM_TV_NSEC
+	    (st.st_mtime < dev->bid_time ||
+	        (st.st_mtime == dev->bid_time &&
+		 st.st_mtim.tv_nsec / 1000 <= dev->bid_utime)) &&
+#else
+	    st.st_mtime <= dev->bid_time &&
+#endif
+	    (diff < BLKID_PROBE_MIN ||
+		(dev->bid_flags & BLKID_BID_FL_VERIFIED &&
+		 diff < BLKID_PROBE_INTERVAL)))
 		return dev;
 
+#ifndef HAVE_STRUCT_STAT_ST_MTIM_TV_NSEC
 	DBG(DEBUG_PROBE,
 	    printf("need to revalidate %s (cache time %lu, stat time %lu,\n\t"
 		   "time since last check %lu)\n",
 		   dev->bid_name, (unsigned long)dev->bid_time,
 		   (unsigned long)st.st_mtime, (unsigned long)diff));
-
+#else
+	DBG(DEBUG_PROBE,
+	    printf("need to revalidate %s (cache time %lu.%lu, stat time %lu.%lu,\n\t"
+		   "time since last check %lu)\n",
+		   dev->bid_name,
+		   (unsigned long)dev->bid_time, (unsigned long)dev->bid_utime,
+		   (unsigned long)st.st_mtime, (unsigned long)st.st_mtim.tv_nsec / 1000,
+		   (unsigned long)diff));
+#endif
 
 	if (!cache->probe) {
 		cache->probe = blkid_new_probe();
@@ -156,8 +172,16 @@ blkid_dev blkid_verify(blkid_cache cache, blkid_dev dev)
 
 found_type:
 	if (dev) {
+#ifdef HAVE_STRUCT_STAT_ST_MTIM_TV_NSEC
+		struct timeval tv;
+		if (!gettimeofday(&tv, NULL)) {
+			dev->bid_time = tv.tv_sec;
+			dev->bid_utime = tv.tv_usec;
+		} else
+#endif
+			dev->bid_time = time(0);
+
 		dev->bid_devno = st.st_rdev;
-		dev->bid_time = time(0);
 		dev->bid_flags |= BLKID_BID_FL_VERIFIED;
 		cache->bic_flags |= BLKID_BIC_FL_CHANGED;