profile library should check high-resolution timestamps if available

With the current profile code, it's possible for a file to be read when
partially written, with the writing of the new file contents being completed
within the same 1-second clock value, causing the profile code not to re-read
the contents.  Using a higher-resolution timestamp, available on many systems
now, should help reduce that window.  (Checking file sizes should also,
consider doing that separately.)

* configure.in: Check struct stat for fields st_mtimensec,
st_mtimespec.tv_nsec, and st_mtim.tv_usec.
* prof_file.c (profile_update_file_data): If one of them is found, use it as
the fractional part of the timestamp.  Do re-read the file if the fractional
parts don't match.
* prof_int.h (struct _prf_data_t): Add new field frac_ts.

ticket: new
status: open

git-svn-id: svn://anonsvn.mit.edu/krb5/trunk@17121 dc483132-0cff-0310-8789-dd5450dbe970

4 files changed, 26 insertions, 1 deletions

diff --git a/src/util/profile/ChangeLog b/src/util/profile/ChangeLog
index 8208db91c..4063b1722 100644
--- a/src/util/profile/ChangeLog
+++ b/src/util/profile/ChangeLog
@@ -1,3 +1,12 @@
+2005-03-13  Ken Raeburn  <raeburn@mit.edu>
+
+	* configure.in: Check struct stat for fields st_mtimensec,
+	st_mtimespec.tv_nsec, and st_mtim.tv_usec.
+	* prof_file.c (profile_update_file_data): If one of them is
+	found, use it as the fractional part of the timestamp.  Do
+	re-read the file if the fractional parts don't match.
+	* prof_int.h (struct _prf_data_t): Add new field frac_ts.
+
 2005-03-03  Ken Raeburn  <raeburn@mit.edu>
 
 	* prof_tree.c (profile_node_iterator): After checking skip_num
diff --git a/src/util/profile/configure.in b/src/util/profile/configure.in
index 38fb9e426..faae28955 100644
--- a/src/util/profile/configure.in
+++ b/src/util/profile/configure.in
@@ -6,6 +6,8 @@ AC_CHECK_SIZEOF(int)
 AC_CHECK_SIZEOF(long)
 AC_CHECK_HEADERS(unistd.h stdlib.h pwd.h)
 AC_CHECK_FUNCS(stat access strdup getpwuid_r)
+AC_CHECK_MEMBERS([struct stat.st_mtimensec,struct stat.st_mtimespec.tv_nsec,struct stat.st_mtim.tv_usec],,,[#include <sys/types.h>
+#include <sys/stat.h>])
 AC_PROG_AWK
 AC_KRB5_TCL
 DO_TCL=
diff --git a/src/util/profile/prof_file.c b/src/util/profile/prof_file.c
index cdeaf50a7..347fef739 100644
--- a/src/util/profile/prof_file.c
+++ b/src/util/profile/prof_file.c
@@ -316,6 +316,7 @@ errcode_t profile_update_file_data(prf_data_t data)
 	errcode_t retval;
 #ifdef HAVE_STAT
 	struct stat st;
+	unsigned long frac;
 #ifdef STAT_ONCE_PER_SECOND
 	time_t now;
 #endif
@@ -342,7 +343,18 @@ errcode_t profile_update_file_data(prf_data_t data)
 #ifdef STAT_ONCE_PER_SECOND
 	data->last_stat = now;
 #endif
-	if (st.st_mtime == data->timestamp && data->root != NULL) {
+#if defined HAVE_STRUCT_STAT_ST_MTIMENSEC
+	frac = st.st_mtimensec;
+#elif defined HAVE_STRUCT_STAT_ST_MTIMESPEC_TV_NSEC
+	frac = st.st_mtimespec.tv_nsec;
+#elif defined HAVE_STRUCT_STAT_ST_MTIM_TV_USEC
+	frac = st.st_mtim.tv_usec;
+#else
+	frac = 0;
+#endif
+	if (st.st_mtime == data->timestamp
+	    && frac == data->frac_ts
+	    && data->root != NULL) {
 	    k5_mutex_unlock(&data->lock);
 	    return 0;
 	}
@@ -387,6 +399,7 @@ errcode_t profile_update_file_data(prf_data_t data)
 	assert(data->root != NULL);
 #ifdef HAVE_STAT
 	data->timestamp = st.st_mtime;
+	data->frac_ts = frac;
 #endif
 	k5_mutex_unlock(&data->lock);
 	return 0;
diff --git a/src/util/profile/prof_int.h b/src/util/profile/prof_int.h
index 43d15b0e4..1a56a3f30 100644
--- a/src/util/profile/prof_int.h
+++ b/src/util/profile/prof_int.h
@@ -42,6 +42,7 @@ struct _prf_data_t {
 	time_t		last_stat;
 #endif
 	time_t		timestamp; /* time tree was last updated from file */
+	unsigned long	frac_ts;   /* fractional part of timestamp, if any */
 	int		flags;	/* r/w, dirty */
 	int		upd_serial; /* incremented when data changes */
 	char		*comment;