[RFC PATCH v1 4/5] selftests/filesystems: add fuse symlink caching test

[Luis Henriques <luis@igalia.com>]

This patch adds a simple test that allows to verify that, when resolving a
symlink, user-space is called only the first time when caching is enabled
or, if caching is disabled, every time the symlink resolution is requested.

Signed-off-by: Luis Henriques <luis@igalia.com>
---
 .../selftests/filesystems/fuse/.gitignore     |   1 +
 .../selftests/filesystems/fuse/Makefile       |   6 +-
 .../selftests/filesystems/fuse/symlink_fs.c   | 115 ++++++++++++++++++
 .../filesystems/fuse/symlink_test.sh          |  52 ++++++++
 4 files changed, 173 insertions(+), 1 deletion(-)
 create mode 100644 tools/testing/selftests/filesystems/fuse/symlink_fs.c
 create mode 100755 tools/testing/selftests/filesystems/fuse/symlink_test.sh

diff --git a/tools/testing/selftests/filesystems/fuse/.gitignore b/tools/testing/selftests/filesystems/fuse/.gitignore
index 3e72e742d08e..cfdc5ca3ded4 100644
--- a/tools/testing/selftests/filesystems/fuse/.gitignore
+++ b/tools/testing/selftests/filesystems/fuse/.gitignore
@@ -1,3 +1,4 @@
 # SPDX-License-Identifier: GPL-2.0-only
 fuse_mnt
 fusectl_test
+symlink_fs
diff --git a/tools/testing/selftests/filesystems/fuse/Makefile b/tools/testing/selftests/filesystems/fuse/Makefile
index 422cd1b1688d..342da0878006 100644
--- a/tools/testing/selftests/filesystems/fuse/Makefile
+++ b/tools/testing/selftests/filesystems/fuse/Makefile
@@ -3,7 +3,8 @@
 CFLAGS += -Wall -O2 -g $(KHDR_INCLUDES)
 
 TEST_GEN_PROGS := fusectl_test
-TEST_GEN_FILES := fuse_mnt
+TEST_PROGS := symlink_test.sh
+TEST_GEN_FILES := fuse_mnt symlink_fs
 
 include ../../lib.mk
 
@@ -19,3 +20,6 @@ endif
 
 $(OUTPUT)/fuse_mnt: CFLAGS += $(VAR_CFLAGS)
 $(OUTPUT)/fuse_mnt: LDLIBS += $(VAR_LDLIBS)
+
+$(OUTPUT)/symlink_fs: CFLAGS += $(VAR_CFLAGS)
+$(OUTPUT)/symlink_fs: LDLIBS += $(VAR_LDLIBS)
diff --git a/tools/testing/selftests/filesystems/fuse/symlink_fs.c b/tools/testing/selftests/filesystems/fuse/symlink_fs.c
new file mode 100644
index 000000000000..1aee26c91b3f
--- /dev/null
+++ b/tools/testing/selftests/filesystems/fuse/symlink_fs.c
@@ -0,0 +1,115 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Simple filesystem to test FUSE symlink cache
+ *
+ * This is a simple FUSE filesystem that contains two objects: a file named
+ * 'file' and a symlink to that file named 'link'.  Whenever the ->readlink() is
+ * executed to resolve 'link' a counter will be incremented.  A ->read() to any
+ * filesystem object will return the value in this counter.
+ *
+ * A '--cache' argument will allow to enable symlink caching (disabled by
+ * default).  This means that, if caching is enabled, resolving a symlink will
+ * only call into user-space the first time.
+ */
+
+#define FUSE_USE_VERSION 31
+
+#include <fuse.h>
+#include <stdio.h>
+#include <string.h>
+#include <errno.h>
+#include <fcntl.h>
+#include <stddef.h>
+#include <assert.h>
+
+#define FILE	"file"
+#define LINK	"link"
+
+static struct options {
+	int cache_symlinks;
+} options;
+
+static const struct fuse_opt option_spec[] = {
+	{ "--cache", offsetof(struct options, cache_symlinks), 1 },
+	FUSE_OPT_END
+};
+
+static int readlink_counter = 0;
+
+static void *symlink_init(struct fuse_conn_info *conn, struct fuse_config *cfg)
+{
+	if (options.cache_symlinks)
+		fuse_set_feature_flag(conn, FUSE_CAP_CACHE_SYMLINKS);
+
+	return NULL;
+}
+
+static int symlink_getattr(const char *path, struct stat *stbuf,
+			   struct fuse_file_info *fi)
+{
+	int res = 0;
+
+	memset(stbuf, 0, sizeof(struct stat));
+	if (strcmp(path, "/") == 0) {
+		stbuf->st_mode = S_IFDIR | 0755;
+		stbuf->st_nlink = 2;
+	} else if (strcmp(path + 1, FILE) == 0) {
+		char data[64];
+
+		stbuf->st_mode = S_IFREG | 0444;
+		stbuf->st_nlink = 1;
+		stbuf->st_size = sprintf(data, "%d\n", readlink_counter);
+	} else if (strcmp(path + 1, LINK) == 0) {
+		stbuf->st_mode = S_IFLNK | 0444;
+		stbuf->st_nlink = 1;
+		stbuf->st_size = strlen(FILE);
+	} else
+		res = -ENOENT;
+
+	return res;
+}
+
+static int symlink_readlink(const char *path, char *buf, size_t size)
+{
+	if (strcmp(path + 1, LINK) != 0)
+		return -ENOENT;
+
+	memcpy(buf, FILE, strlen(FILE));
+	readlink_counter++;
+
+	return 0;
+}
+
+static int symlink_read(const char *path, char *buf, size_t sz, off_t off,
+			struct fuse_file_info *fi)
+{
+	char data[64];
+	int len;
+
+	len = sprintf(data, "%d\n", readlink_counter);
+	memcpy(buf, data, len);
+
+	return len;
+}
+
+static const struct fuse_operations symlink_oper = {
+	.init           = symlink_init,
+	.getattr	= symlink_getattr,
+	.readlink	= symlink_readlink,
+	.read		= symlink_read,
+};
+
+int main(int argc, char *argv[])
+{
+	int ret;
+	struct fuse_args args = FUSE_ARGS_INIT(argc, argv);
+
+	options.cache_symlinks = 0;
+	if (fuse_opt_parse(&args, &options, option_spec, NULL) == -1)
+		return 1;
+
+	ret = fuse_main(args.argc, args.argv, &symlink_oper, NULL);
+	fuse_opt_free_args(&args);
+
+	return ret;
+}
diff --git a/tools/testing/selftests/filesystems/fuse/symlink_test.sh b/tools/testing/selftests/filesystems/fuse/symlink_test.sh
new file mode 100755
index 000000000000..546541c1920e
--- /dev/null
+++ b/tools/testing/selftests/filesystems/fuse/symlink_test.sh
@@ -0,0 +1,52 @@
+#!/bin/sh
+# SPDX-License-Identifier: GPL-2.0
+
+exit_cleanup()
+{
+	fusermount -u ./mnt
+	rmdir ./mnt
+}
+
+assert_value ()
+{
+	if [ $1 -ne $2 ]; then
+		echo "FAILED"
+		echo $3
+		exit 1
+	fi
+}
+
+set -e
+
+trap exit_cleanup EXIT
+
+mkdir -p mnt
+
+./symlink_fs ./mnt
+
+echo -n "Testing symlink without cached: "
+
+# When symlink caching is disabled every access to a symlink is expected to
+# result in a call to user-space
+for i in $(seq 1 10); do
+	readlink ./mnt/link > /dev/null
+done
+
+res=$(cat ./mnt/file)
+assert_value $res $i "Got $res, expected $i"
+echo "PASSED"
+
+fusermount -u ./mnt
+
+./symlink_fs --cache ./mnt
+
+echo -n "Testing symlink with cache: "
+
+# With caching enabled, there will only be a single call into user-space
+for i in $(seq 0 10); do
+	readlink ./mnt/link > /dev/null
+done
+
+res=$(cat ./mnt/file)
+assert_value 1 $res "Got $ res, expected 1"
+echo "PASSED"