lib-fs: Added fs_get_nlinks()

Although fs_stat() could return this, its caller can't indicate whether
it actually wants the link count. Usually fs_stat() is used only to get
the file's size. In some backends it's not cheap to get the link count,
so adding this function allows the caller to explicitly ask for it.

src/lib-fs/fs-api-private.h

@@ -69,6 +69,7 @@ struct fs_vfuncs {
 	int (*iter_deinit)(struct fs_iter *iter);
 
 	bool (*switch_ioloop)(struct fs *fs);
+	int (*get_nlinks)(struct fs_file *file, nlink_t *nlinks_r);
 };
 
 struct fs {

src/lib-fs/fs-api.c

@@ -848,6 +848,33 @@ int fs_stat(struct fs_file *file, struct stat *st_r)
 	return ret;
 }
 
+int fs_get_nlinks(struct fs_file *file, nlink_t *nlinks_r)
+{
+	int ret;
+
+	if (file->fs->v.get_nlinks == NULL) {
+		struct stat st;
+
+		if (fs_stat(file, &st) < 0)
+			return -1;
+		*nlinks_r = st.st_nlink;
+		return 0;
+	}
+
+	if (!file->read_or_prefetch_counted &&
+	    !file->lookup_metadata_counted && !file->stat_counted) {
+		file->stat_counted = TRUE;
+		file->fs->stats.stat_count++;
+		fs_file_timing_start(file, FS_OP_STAT);
+	}
+	T_BEGIN {
+		ret = file->fs->v.get_nlinks(file, nlinks_r);
+	} T_END;
+	if (!(ret < 0 && errno == EAGAIN))
+		fs_file_timing_end(file, FS_OP_STAT);
+	return ret;
+}
+
 int fs_default_copy(struct fs_file *src, struct fs_file *dest)
 {
 	/* we're going to be counting this as read+write, so remove the

src/lib-fs/fs-api.h

@@ -303,6 +303,10 @@ int fs_delete(struct fs_file *file);
 /* Returns 0 if ok, -1 if error occurred (e.g. errno=ENOENT).
    All fs backends may not support all stat fields. */
 int fs_stat(struct fs_file *file, struct stat *st_r);
+/* Get number of links to the file. This is the same as using fs_stat()'s
+   st_nlinks field, except not all backends support returning it via fs_stat().
+   Returns 0 if ok, -1 if error occurred. */
+int fs_get_nlinks(struct fs_file *file, nlink_t *nlinks_r);
 /* Copy an object with possibly updated metadata. Destination parent
    directories are created automatically. Returns 0 if ok, -1 if error
    occurred. */

src/lib-fs/fs-dict.c

@@ -323,6 +323,7 @@ const struct fs fs_class_dict = {
 		fs_dict_iter_init,
 		fs_dict_iter_next,
 		fs_dict_iter_deinit,
+		NULL,
 		NULL
 	}
 };

src/lib-fs/fs-metawrap.c

@@ -496,6 +496,7 @@ const struct fs fs_class_metawrap = {
 		fs_wrapper_iter_init,
 		fs_wrapper_iter_next,
 		fs_wrapper_iter_deinit,
-		NULL
+		NULL,
+		fs_wrapper_get_nlinks,
 	}
 };

src/lib-fs/fs-posix.c

@@ -884,6 +884,7 @@ const struct fs fs_class_posix = {
 		fs_posix_iter_init,
 		fs_posix_iter_next,
 		fs_posix_iter_deinit,
-		NULL
+		NULL,
+		NULL,
 	}
 };

src/lib-fs/fs-randomfail.c

@@ -446,6 +446,17 @@ static int fs_randomfail_stat(struct fs_file *_file, struct stat *st_r)
 	return fs_file_random_fail_end(file, ret, FS_OP_STAT);
 }
 
+static int fs_randomfail_get_nlinks(struct fs_file *_file, nlink_t *nlinks_r)
+{
+	struct randomfail_fs_file *file = (struct randomfail_fs_file *)_file;
+	int ret;
+
+	if (fs_file_random_fail_begin(file, FS_OP_STAT))
+		return -1;
+	ret = fs_get_nlinks(file->super, nlinks_r);
+	return fs_file_random_fail_end(file, ret, FS_OP_STAT);
+}
+
 static int fs_randomfail_copy(struct fs_file *_src, struct fs_file *_dest)
 {
 	struct randomfail_fs_file *src = (struct randomfail_fs_file *)_src;
@@ -566,6 +577,7 @@ const struct fs fs_class_randomfail = {
 		fs_randomfail_iter_init,
 		fs_randomfail_iter_next,
 		fs_randomfail_iter_deinit,
-		NULL
+		NULL,
+		fs_randomfail_get_nlinks,
 	}
 };

src/lib-fs/fs-sis-queue.c

@@ -200,6 +200,7 @@ const struct fs fs_class_sis_queue = {
 		fs_wrapper_iter_init,
 		NULL,
 		NULL,
-		NULL
+		NULL,
+		fs_wrapper_get_nlinks,
 	}
 };

src/lib-fs/fs-sis.c

@@ -351,6 +351,7 @@ const struct fs fs_class_sis = {
 		fs_wrapper_iter_init,
 		NULL,
 		NULL,
-		NULL
+		NULL,
+		fs_wrapper_get_nlinks,
 	}
 };

src/lib-fs/fs-test.c

@@ -417,6 +417,7 @@ const struct fs fs_class_test = {
 		fs_test_iter_init,
 		fs_test_iter_next,
 		fs_test_iter_deinit,
-		NULL
+		NULL,
+		NULL,
 	}
 };

src/lib-fs/fs-wrapper.c

@@ -108,6 +108,11 @@ int fs_wrapper_stat(struct fs_file *file, struct stat *st_r)
 	return fs_stat(file->parent, st_r);
 }
 
+int fs_wrapper_get_nlinks(struct fs_file *file, nlink_t *nlinks_r)
+{
+	return fs_get_nlinks(file->parent, nlinks_r);
+}
+
 int fs_wrapper_copy(struct fs_file *src, struct fs_file *dest)
 {
 	if (src != NULL)

src/lib-fs/fs-wrapper.h

@@ -24,6 +24,7 @@ int fs_wrapper_lock(struct fs_file *file, unsigned int secs,
 void fs_wrapper_unlock(struct fs_lock *_lock);
 int fs_wrapper_exists(struct fs_file *file);
 int fs_wrapper_stat(struct fs_file *file, struct stat *st_r);
+int fs_wrapper_get_nlinks(struct fs_file *file, nlink_t *nlinks_r);
 int fs_wrapper_copy(struct fs_file *src, struct fs_file *dest);
 int fs_wrapper_rename(struct fs_file *src, struct fs_file *dest);
 int fs_wrapper_delete(struct fs_file *file);

src/plugins/fs-compress/fs-compress.c

@@ -254,6 +254,7 @@ const struct fs fs_class_compress = {
 		fs_wrapper_iter_init,
 		fs_wrapper_iter_next,
 		fs_wrapper_iter_deinit,
-		NULL
+		NULL,
+		fs_wrapper_get_nlinks
 	}
 };