Use O_NOATIME when opening the sha1 files.

We really don't care about atime, and it sucks to dirty the
inode cache just for it.

This is more than a one-liner only because we need to be able to
clear the O_NOATIME flag in case some of the objects are owned
by others (in which case open will return EPERM), and because not
everybody has the O_NOATIME flag.

diff --git a/sha1_file.c b/sha1_file.c
index 6f7228e106d4e24b18f8416cc6adc2a6fd303eb7..66308ede85c2dad6b184fb74a7215b06a173d8f7 100644 (file)
--- a/sha1_file.c
+++ b/sha1_file.c
@@ -11,6 +11,16 @@
 
 const char *sha1_file_directory = NULL;
 
+#ifndef O_NOATIME
+#if defined(__linux__) && (defined(__i386__) || defined(__PPC__))
+#define O_NOATIME 01000000
+#else
+#define O_NOATIME 0
+#endif
+#endif
+
+static unsigned int sha1_file_open_flag = O_NOATIME;
+
 static unsigned hexval(char c)
 {
        if (c >= '0' && c <= '9')
@@ -96,13 +106,26 @@ int check_sha1_signature(unsigned char *sha1, void *map, unsigned long size, con
 void *map_sha1_file(const unsigned char *sha1, unsigned long *size)
 {
        char *filename = sha1_file_name(sha1);
-       int fd = open(filename, O_RDONLY);
        struct stat st;
        void *map;
+       int fd;
 
+       fd = open(filename, O_RDONLY | sha1_file_open_flag);
        if (fd < 0) {
-               perror(filename);
-               return NULL;
+               /* See if it works without O_NOATIME */
+               switch (sha1_file_open_flag) {
+               default:
+                       fd = open(filename, O_RDONLY);
+                       if (fd >= 0)
+                               break;
+               /* Fallthrough */
+               case 0:
+                       perror(filename);
+                       return NULL;
+               }
+
+               /* If it failed once, it will probably fail again. Stop using O_NOATIME */
+               sha1_file_open_flag = 0;
        }
        if (fstat(fd, &st) < 0) {
                close(fd);