Re: [PATCH 10/25] vfs: fsinfo sample: Mount listing program [ver #13]

From: Alan Jenkins
Date: Wed Jun 05 2019 - 08:26:17 EST

On 28/05/2019 16:12, David Howells wrote:
Implement a program to demonstrate mount listing using the new fsinfo()
syscall,

Great. I understand this is only for demonstration, but IMO the output would be clearer with a few tweaks:

for example:

# ./test-mntinfo

Can we have a header please? E.g.

MNT ID NOTIFS TYPE DEVICE
-------------------------------------- -------- -------- ---- ------


ROOT 5d c ext4 8:12
\_ sys 13 8 sysfs 0:13
| \_ kernel/security 16 0 securityfs 0:7

I assume ID is the same ID which is shown in /proc/mounts. But it's shown as decimal there. Can we match that?

And can we show NOTIFS in decimal as well? I find counters easier to read in decimal :-).

I.e. change "%8x" to "%10d" in both cases.

major:minor is also more often seen formatted as "%d:%d": in /proc/self/mountinfo, lsblk, and ls -l. I don't feel as strongly about this one though.

Thanks
Alan

| \_ fs/cgroup 1a 10 tmpfs 0:17
| | \_ unified 1b 0 cgroup2 0:18
| | \_ systemd 1c 0 cgroup 0:19
| | \_ freezer 20 0 cgroup 0:1d
| | \_ cpu,cpuacct 21 0 cgroup 0:1e
| | \_ memory 22 0 cgroup 0:1f
| | \_ cpuset 23 0 cgroup 0:20
| | \_ hugetlb 24 0 cgroup 0:21
| | \_ net_cls,net_prio 25 0 cgroup 0:22
| | \_ blkio 26 0 cgroup 0:23
| | \_ perf_event 27 0 cgroup 0:24
| | \_ devices 28 0 cgroup 0:25
| | \_ rdma 29 0 cgroup 0:26
| \_ fs/pstore 1d 0 pstore 0:1a
| \_ firmware/efi/efivars 1e 0 efivarfs 0:1b
| \_ fs/bpf 1f 0 bpf 0:1c
| \_ kernel/config 5a 0 configfs 0:10
| \_ fs/selinux 2a 0 selinuxfs 0:12
| \_ kernel/debug 2e 0 debugfs 0:8
\_ dev 15 4 devtmpfs 0:6
| \_ shm 17 0 tmpfs 0:14
| \_ pts 18 0 devpts 0:15
| \_ hugepages 2b 0 hugetlbfs 0:27
| \_ mqueue 2c 0 mqueue 0:11
\_ run 19 1 tmpfs 0:16
| \_ user/0 1b4 0 tmpfs 0:2d
\_ proc 14 1 proc 0:4
| \_ sys/fs/binfmt_misc 2d 0 autofs 0:28
\_ tmp 2f 7d0 tmpfs 0:29
\_ var/cache/fscache 71 0 tmpfs 0:2a
\_ boot 74 0 ext4 8:15
\_ home 74 0 ext4 8:15
\_ var/lib/nfs/rpc_pipefs bf 0 rpc_pipefs 0:2b
\_ mnt 15b 5 tmpfs 0:2c
| \_ foo 164 0 tmpfs 0:2e
| \_ foo1 16d 0 tmpfs 0:2f
| \_ foo2 176 0 tmpfs 0:30
| \_ foo3 17f 0 tmpfs 0:31
| \_ foo4 188 1 tmpfs 0:32
| \_ "" 191 0 tmpfs 0:33
\_ afs 19a 2 afs 0:34
\_ procyon.org.uk 1a3 0 afs 0:35
\_ grand.central.org 1ac 0 afs 0:36

Signed-off-by: David Howells<dhowells@xxxxxxxxxx>
---

samples/vfs/Makefile | 3 +
samples/vfs/test-mntinfo.c | 239 ++++++++++++++++++++++++++++++++++++++++++++
2 files changed, 242 insertions(+)
create mode 100644 samples/vfs/test-mntinfo.c

diff --git a/samples/vfs/test-mntinfo.c b/samples/vfs/test-mntinfo.c
new file mode 100644
index 000000000000..00fbefae98fa
--- /dev/null
+++ b/samples/vfs/test-mntinfo.c

+/*
+ * 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_child *children;
+ struct fsinfo_mount_info info;
+ struct fsinfo_ids ids;
+ unsigned int d;
+ size_t ch_size, p_size;
+ int i, n, s;
+
+ get_attr(mnt_id, FSINFO_ATTR_MOUNT_INFO, &info, sizeof(info));
+ get_attr(mnt_id, FSINFO_ATTR_IDS, &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 < 40)
+ s = 40 - s;
+ else
+ s = 1;
+ printf("%*.*s", s, s, "");
+
+ printf("%8x %8x %s %x:%x",
+ info.mnt_id, info.notify_counter,
+ ids.f_fs_name, ids.f_dev_major, ids.f_dev_minor);
+ putchar('\n');
+
+ children = get_attr_alloc(mnt_id, FSINFO_ATTR_MOUNT_CHILDREN, 0, &ch_size);
+ n = ch_size / sizeof(children[0]) - 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;
+
+ for (i = 0; i < n; i++) {
+ if (i == n - 1)
+ bar_buf[depth + 1] = ' ';
+ path = get_attr_alloc(mnt_id, FSINFO_ATTR_MOUNT_SUBMOUNT, i, &p_size);
+ display_mount(children[i].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 = {
+ .request = FSINFO_ATTR_MOUNT_INFO,
+ };
+
+ if (fsinfo(AT_FDCWD, path, &params, &mnt, sizeof(mnt)) == -1) {
+ perror(path);
+ exit(1);
+ }
+
+ return mnt.mnt_id;
+}
+
+/*
+ *
+ */
+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);
+ }
+
+ display_mount(mnt_id, 0, path);
+ return 0;
+}