Added option --no-user-group-precaching

ChangeLog

@@ -1,3 +1,7 @@
+2018-01-15  Martin Pärtel <martin dot partel at gmail dot com>
+
+	* Added option --no-user-group-precaching (issue #62).
+
 2017-11-30  Martin Pärtel <martin dot partel at gmail dot com>
 
 	* Added options --delete-deny and --rename-deny as suggested by @roojs.

src/bindfs.1

@@ -360,6 +360,14 @@ ioctl. This may be a security concern, especially when mounting as root.
 .B \-\-block\-devices\-as\-files, \-o block\-devices\-as\-files
 Shows block devices as regular files.
 
+.TP
+.B \-\-no\-user\-group\-precaching, \-o no\-user\-group\-precaching
+Disables the default behaviour of caching users and their group memberships
+at startup. Instead they are read and then cached indefinitely on-demand.
+Sending bindfs \fBSIGUSR1\fP will clear this cache in either case.
+
+Currently this cache is only used by \fB\-\-mirror\fP and \fB\-\-mirror\-only\fP.
+
 .TP
 .B \-\-multithreaded, \-o multithreaded
 Run bindfs in multithreaded mode. While bindfs is designed to be

src/bindfs.c

@@ -1486,6 +1486,7 @@ static void print_usage(const char *progname)
            "  --resolve-symlinks        Resolve symbolic links.\n"
            "  --resolved-symlink-deletion=...  Decide how to delete resolved symlinks.\n"
            "  --block-devices-as-files  Show block devices as regular files.\n"
+           "  --no-user-group-precaching Don't read all users and groups at startup.\n"
            "  --multithreaded           Enable multithreaded mode. See man page\n"
            "                            for security issue with current implementation.\n"
            "\n"
@@ -1846,11 +1847,14 @@ static void setup_signal_handling()
 
 static void signal_handler(int sig)
 {
-    invalidate_user_cache();
+    invalidate_user_caches();
 }
 
 static void atexit_func()
 {
+    // This cleanup is mostly unnecessary, but we do it anyway to
+    // reduce the "still reachable" allocations that Valgrind shows.
+
     free(settings.mntsrc);
     free(settings.mntdest);
     free(settings.original_working_dir);
@@ -1879,6 +1883,8 @@ static void atexit_func()
     settings.mirrored_users = NULL;
     free(settings.mirrored_members);
     settings.mirrored_members = NULL;
+
+    clear_user_caches();
 }
 
 int main(int argc, char *argv[])
@@ -1903,6 +1909,7 @@ int main(int argc, char *argv[])
         char *chmod_filter;
         char *resolved_symlink_deletion;
         int no_allow_other;
+        int no_user_group_precaching;
         int multithreaded;
         char *uid_offset;
         char *gid_offset;
@@ -1974,13 +1981,11 @@ int main(int argc, char *argv[])
         OPT2("--enable-lock-forwarding", "enable-lock-forwarding", OPTKEY_ENABLE_LOCK_FORWARDING),
         OPT2("--disable-lock-forwarding", "disable-lock-forwarding", OPTKEY_DISABLE_LOCK_FORWARDING),
         OPT2("--enable-ioctl", "enable-ioctl", OPTKEY_ENABLE_IOCTL),
+        OPT_OFFSET2("--no-user-group-precaching", "no-user-group-precaching", no_user_group_precaching, -1),
         OPT_OFFSET2("--multithreaded", "multithreaded", multithreaded, -1),
         OPT_OFFSET2("--uid-offset=%s", "uid-offset=%s", uid_offset, 0),
         OPT_OFFSET2("--gid-offset=%s", "gid-offset=%s", gid_offset, 0),
-
-
-
-
+
         FUSE_OPT_END
     };
 
@@ -2176,6 +2181,11 @@ int main(int argc, char *argv[])
         }
     }
 
+    /* Precache entire user/group database for use by --mirror by default */
+    if (!od.no_user_group_precaching) {
+        rebuild_user_caches();
+    }
+
     /* Parse permission bits */
     if (od.perms) {
         if (add_chmod_rules_to_permchain(od.perms, settings.permchain) != 0) {

src/misc.c

@@ -135,6 +135,30 @@ const char *my_dirname(char *path)
     }
 }
 
+void insertion_sort_last(void *base, size_t nmemb, size_t size, int (*compar)(const void*, const void*))
+{
+    void *const last = base + (nmemb - 1) * size;
+    void *const entry = malloc(size);
+    memcpy(entry, last, size);
+
+    // Find the location to insert at.
+    int n = 0;
+    void *p = last - size;
+    while (p >= base && compar(entry, p) < 0) {
+        p -= size;
+        n += 1;
+    }
+
+    // We found a *p that's larger or we went below the start of the array, so go back one step.
+    p += size;
+    // No need to adjust n, it's now the correct number of elements to shift forward
+
+    // Insert at *p.
+    memmove(p + size, p, n * size);
+    memcpy(p, entry, size);
+    free(entry);
+}
+
 void grow_array_impl(void **array, int *capacity, int member_size)
 {
     int new_cap = *capacity;

src/misc.h

@@ -20,6 +20,7 @@
 #ifndef INC_BINDFS_MISC_H
 #define INC_BINDFS_MISC_H
 
+#include <stdlib.h>
 
 /* Counts the number of times ch occurs in s. */
 int count_chars(const char *s, char ch);
@@ -49,6 +50,10 @@ const char *my_basename(const char *path);
    Otherwise, returns ".". */
 const char *my_dirname(char *path);
 
+/* Sorts an array that is otherwise sorted, but whose last element may be in the wrong place.
+   The signature is the same as qsort's. */
+void insertion_sort_last(void *base, size_t nmemb, size_t size, int (*compar)(const void*, const void*));
+
 /* Reallocs `*array` (may be NULL) to be at least one larger
    than `*capacity` (may be 0) and stores the new capacity
    in `*capacity`. */