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Subject[PATCH 09/13] fsinfo: sample: Mount listing program [ver #19]
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Date
Implement a program to demonstrate mount listing using the new fsinfo()
syscall. For example, to dump the tree from mount 21:

# ./test-mntinfo -m 21
MOUNT MOUNT ID CHANGE# AT P DEV TYPE
-------------------------------- ---------- -------- -- - ----- --------
21 21 0 e 4 0:14 sysfs
\_ kernel/security 24 0 e 4 0:8 securityfs
\_ fs/cgroup 28 4 2f 4 0:18 tmpfs
| \_ unified 29 0 e 4 0:19 cgroup2
| \_ systemd 30 0 e 4 0:1a cgroup
| \_ blkio 34 0 e 4 0:1e cgroup
| \_ net_cls,net_prio 35 0 e 4 0:1f cgroup
| \_ perf_event 36 0 e 4 0:20 cgroup
| \_ freezer 37 0 e 4 0:21 cgroup
| \_ devices 38 0 e 4 0:22 cgroup
| \_ cpu,cpuacct 39 0 e 4 0:23 cgroup
| \_ rdma 40 0 e 4 0:24 cgroup
| \_ memory 41 0 e 4 0:25 cgroup
| \_ cpuset 42 0 e 4 0:26 cgroup
| \_ hugetlb 43 0 e 4 0:27 cgroup
\_ fs/pstore 31 0 e 4 0:1b pstore
\_ firmware/efi/efivars 32 0 e 4 0:1c efivarfs
\_ fs/bpf 33 0 e 4 0:1d bpf
\_ kernel/config 92 0 0 4 0:28 configfs
\_ fs/selinux 44 0 0 4 0:11 selinuxfs
\_ kernel/debug 45 1 0 4 0:7 debugfs

Signed-off-by: David Howells <dhowells@redhat.com>
---

samples/vfs/Makefile | 2
samples/vfs/test-mntinfo.c | 279 ++++++++++++++++++++++++++++++++++++++++++++
2 files changed, 281 insertions(+)
create mode 100644 samples/vfs/test-mntinfo.c

diff --git a/samples/vfs/Makefile b/samples/vfs/Makefile
index 9159ad1d7fc5..19be60ab950e 100644
--- a/samples/vfs/Makefile
+++ b/samples/vfs/Makefile
@@ -4,12 +4,14 @@
hostprogs := \
test-fsinfo \
test-fsmount \
+ test-mntinfo \
test-statx

always-y := $(hostprogs)

HOSTCFLAGS_test-fsinfo.o += -I$(objtree)/usr/include
HOSTLDLIBS_test-fsinfo += -static -lm
+HOSTCFLAGS_test-mntinfo.o += -I$(objtree)/usr/include

HOSTCFLAGS_test-fsmount.o += -I$(objtree)/usr/include
HOSTCFLAGS_test-statx.o += -I$(objtree)/usr/include
diff --git a/samples/vfs/test-mntinfo.c b/samples/vfs/test-mntinfo.c
new file mode 100644
index 000000000000..d7e9942a70d6
--- /dev/null
+++ b/samples/vfs/test-mntinfo.c
@@ -0,0 +1,279 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/* Test the fsinfo() system call
+ *
+ * Copyright (C) 2020 Red Hat, Inc. All Rights Reserved.
+ * Written by David Howells (dhowells@redhat.com)
+ */
+
+#define _GNU_SOURCE
+#define _ATFILE_SOURCE
+#include <stdbool.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <stdint.h>
+#include <string.h>
+#include <unistd.h>
+#include <ctype.h>
+#include <errno.h>
+#include <time.h>
+#include <math.h>
+#include <sys/syscall.h>
+#include <linux/fsinfo.h>
+#include <linux/socket.h>
+#include <linux/fcntl.h>
+#include <sys/stat.h>
+#include <arpa/inet.h>
+
+#ifndef __NR_fsinfo
+#define __NR_fsinfo -1
+#endif
+
+static __attribute__((unused))
+ssize_t fsinfo(int dfd, const char *filename,
+ struct fsinfo_params *params, size_t params_size,
+ void *result_buffer, size_t result_buf_size)
+{
+ return syscall(__NR_fsinfo, dfd, filename,
+ params, params_size,
+ result_buffer, result_buf_size);
+}
+
+static char tree_buf[4096];
+static char bar_buf[4096];
+static unsigned int children_list_interval;
+
+/*
+ * Get an fsinfo attribute in a statically allocated buffer.
+ */
+static void get_attr(unsigned int mnt_id, unsigned int attr, unsigned int Nth,
+ void *buf, size_t buf_size)
+{
+ struct fsinfo_params params = {
+ .flags = FSINFO_FLAGS_QUERY_MOUNT,
+ .request = attr,
+ .Nth = Nth,
+ };
+ char file[32];
+ long ret;
+
+ sprintf(file, "%u", mnt_id);
+
+ memset(buf, 0xbd, buf_size);
+
+ ret = fsinfo(AT_FDCWD, file, &params, sizeof(params), buf, buf_size);
+ if (ret == -1) {
+ fprintf(stderr, "mount-%s: %m\n", file);
+ exit(1);
+ }
+}
+
+/*
+ * Get an fsinfo attribute in a dynamically allocated buffer.
+ */
+static void *get_attr_alloc(unsigned int mnt_id, unsigned int attr,
+ unsigned int Nth, size_t *_size)
+{
+ struct fsinfo_params params = {
+ .flags = FSINFO_FLAGS_QUERY_MOUNT,
+ .request = attr,
+ .Nth = Nth,
+ };
+ size_t buf_size = 4096;
+ char file[32];
+ void *r;
+ long ret;
+
+ sprintf(file, "%u", mnt_id);
+
+ for (;;) {
+ r = malloc(buf_size);
+ if (!r) {
+ perror("malloc");
+ exit(1);
+ }
+ memset(r, 0xbd, buf_size);
+
+ ret = fsinfo(AT_FDCWD, file, &params, sizeof(params), r, buf_size);
+ if (ret == -1) {
+ fprintf(stderr, "mount-%s: %x,%x,%x %m\n",
+ file, params.request, params.Nth, params.Mth);
+ exit(1);
+ }
+
+ if (ret <= buf_size) {
+ *_size = ret;
+ break;
+ }
+ buf_size = (ret + 4096 - 1) & ~(4096 - 1);
+ }
+
+ return r;
+}
+
+/*
+ * Display a mount and then recurse through its children.
+ */
+static void display_mount(unsigned int mnt_id, unsigned int depth, char *path)
+{
+ struct fsinfo_mount_topology top;
+ struct fsinfo_mount_child child;
+ struct fsinfo_mount_info info;
+ struct fsinfo_ids ids;
+ void *children;
+ unsigned int d;
+ size_t ch_size, p_size;
+ char dev[64];
+ int i, n, s;
+
+ get_attr(mnt_id, FSINFO_ATTR_MOUNT_TOPOLOGY, 0, &top, sizeof(top));
+ get_attr(mnt_id, FSINFO_ATTR_MOUNT_INFO, 0, &info, sizeof(info));
+ get_attr(mnt_id, FSINFO_ATTR_IDS, 0, &ids, sizeof(ids));
+ if (depth > 0)
+ printf("%s", tree_buf);
+
+ s = strlen(path);
+ printf("%s", !s ? "\"\"" : path);
+ if (!s)
+ s += 2;
+ s += depth;
+ if (s < 38)
+ s = 38 - s;
+ else
+ s = 1;
+ printf("%*.*s", s, s, "");
+
+ sprintf(dev, "%x:%x", ids.f_dev_major, ids.f_dev_minor);
+ printf("%10u %8x %2x %x %5s %s",
+ info.mnt_id,
+ (info.sb_changes +
+ info.sb_notifications +
+ info.mnt_attr_changes +
+ info.mnt_topology_changes +
+ info.mnt_subtree_notifications),
+ info.attr, top.propagation,
+ dev, ids.f_fs_name);
+ putchar('\n');
+
+ children = get_attr_alloc(mnt_id, FSINFO_ATTR_MOUNT_CHILDREN, 0, &ch_size);
+ n = ch_size / children_list_interval - 1;
+
+ bar_buf[depth + 1] = '|';
+ if (depth > 0) {
+ tree_buf[depth - 4 + 1] = bar_buf[depth - 4 + 1];
+ tree_buf[depth - 4 + 2] = ' ';
+ }
+
+ tree_buf[depth + 0] = ' ';
+ tree_buf[depth + 1] = '\\';
+ tree_buf[depth + 2] = '_';
+ tree_buf[depth + 3] = ' ';
+ tree_buf[depth + 4] = 0;
+ d = depth + 4;
+
+ memset(&child, 0, sizeof(child));
+ for (i = 0; i < n; i++) {
+ void *p = children + i * children_list_interval;
+
+ if (sizeof(child) >= children_list_interval)
+ memcpy(&child, p, children_list_interval);
+ else
+ memcpy(&child, p, sizeof(child));
+
+ if (i == n - 1)
+ bar_buf[depth + 1] = ' ';
+ path = get_attr_alloc(child.mnt_id, FSINFO_ATTR_MOUNT_POINT,
+ 0, &p_size);
+ display_mount(child.mnt_id, d, path + 1);
+ free(path);
+ }
+
+ free(children);
+ if (depth > 0) {
+ tree_buf[depth - 4 + 1] = '\\';
+ tree_buf[depth - 4 + 2] = '_';
+ }
+ tree_buf[depth] = 0;
+}
+
+/*
+ * Find the ID of whatever is at the nominated path.
+ */
+static unsigned int lookup_mnt_by_path(const char *path)
+{
+ struct fsinfo_mount_info mnt;
+ struct fsinfo_params params = {
+ .flags = FSINFO_FLAGS_QUERY_PATH,
+ .request = FSINFO_ATTR_MOUNT_INFO,
+ };
+
+ if (fsinfo(AT_FDCWD, path, &params, sizeof(params), &mnt, sizeof(mnt)) == -1) {
+ perror(path);
+ exit(1);
+ }
+
+ return mnt.mnt_id;
+}
+
+/*
+ * Determine the element size for the mount child list.
+ */
+static unsigned int query_list_element_size(int mnt_id, unsigned int attr)
+{
+ struct fsinfo_attribute_info attr_info;
+
+ get_attr(mnt_id, FSINFO_ATTR_FSINFO_ATTRIBUTE_INFO, attr,
+ &attr_info, sizeof(attr_info));
+ return attr_info.size;
+}
+
+/*
+ *
+ */
+int main(int argc, char **argv)
+{
+ unsigned int mnt_id;
+ char *path;
+ bool use_mnt_id = false;
+ int opt;
+
+ while ((opt = getopt(argc, argv, "m"))) {
+ switch (opt) {
+ case 'm':
+ use_mnt_id = true;
+ continue;
+ }
+ break;
+ }
+
+ argc -= optind;
+ argv += optind;
+
+ switch (argc) {
+ case 0:
+ mnt_id = lookup_mnt_by_path("/");
+ path = "ROOT";
+ break;
+ case 1:
+ path = argv[0];
+ if (use_mnt_id) {
+ mnt_id = strtoul(argv[0], NULL, 0);
+ break;
+ }
+
+ mnt_id = lookup_mnt_by_path(argv[0]);
+ break;
+ default:
+ printf("Format: test-mntinfo\n");
+ printf("Format: test-mntinfo <path>\n");
+ printf("Format: test-mntinfo -m <mnt_id>\n");
+ exit(2);
+ }
+
+ children_list_interval =
+ query_list_element_size(mnt_id, FSINFO_ATTR_MOUNT_CHILDREN);
+
+ printf("MOUNT MOUNT ID CHANGE# AT P DEV TYPE\n");
+ printf("------------------------------------- ---------- -------- -- - ----- --------\n");
+ display_mount(mnt_id, 0, path);
+ return 0;
+}

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