Now that open_by_handle_at(2) can return u64 mount IDs, do some tests to
make sure they match properly as part of the regular open_by_handle
tests.

Link: https://lore.kernel.org/all/20240801-exportfs-u64-mount-id-v3-0-be5d6283144a@cyphar.com/ (local)
Signed-off-by: Aleksa Sarai <redacted>
---
 src/open_by_handle.c | 123 ++++++++++++++++++++++++++++++++-----------
 tests/generic/426    |   1 +
 2 files changed, 93 insertions(+), 31 deletions(-)

diff --git a/src/open_by_handle.c b/src/open_by_handle.c
index d9c802ca9bd1..cbd68aeadac1 100644
--- a/src/open_by_handle.c
+++ b/src/open_by_handle.c

@@ -86,10 +86,15 @@ Examples:
 #include <errno.h>
 #include <linux/limits.h>
 #include <libgen.h>
+#include <stdint.h>

 #include <sys/stat.h>
 #include "statx.h"

+#ifndef AT_HANDLE_MNT_ID_UNIQUE
+#      define AT_HANDLE_MNT_ID_UNIQUE 0x001
+#endif
+
 #define MAXFILES 1024

 struct handle {

@@ -99,7 +104,7 @@ struct handle {

 void usage(void)
 {
-       fprintf(stderr, "usage: open_by_handle [-cludmrwapknhs] [<-i|-o> <handles_file>] <test_dir> [num_files]\n");
+       fprintf(stderr, "usage: open_by_handle [-cludMmrwapknhs] [<-i|-o> <handles_file>] <test_dir> [num_files]\n");
        fprintf(stderr, "\n");
        fprintf(stderr, "open_by_handle -c <test_dir> [N] - create N test files under test_dir, try to get file handles and exit\n");
        fprintf(stderr, "open_by_handle    <test_dir> [N] - get file handles of test files, drop caches and try to open by handle\n");

@@ -111,6 +116,7 @@ void usage(void)
        fprintf(stderr, "open_by_handle -l <test_dir> [N] - create hardlinks to test files, drop caches and try to open by handle\n");
        fprintf(stderr, "open_by_handle -u <test_dir> [N] - unlink (hardlinked) test files, drop caches and try to open by handle\n");
        fprintf(stderr, "open_by_handle -d <test_dir> [N] - unlink test files and hardlinks, drop caches and try to open by handle\n");
+       fprintf(stderr, "open_by_handle -M <test_dir> [N] - confirm that the mount id returned by name_to_handle_at matches the mount id in statx\n");
        fprintf(stderr, "open_by_handle -m <test_dir> [N] - rename test files, drop caches and try to open by handle\n");
        fprintf(stderr, "open_by_handle -p <test_dir>     - create/delete and try to open by handle also test_dir itself\n");
        fprintf(stderr, "open_by_handle -i <handles_file> <test_dir> [N] - read test files handles from file and try to open by handle\n");

@@ -120,6 +126,81 @@ void usage(void)
        exit(EXIT_FAILURE);
 }

+int do_name_to_handle_at(const char *fname, struct file_handle *fh, int bufsz,
+                        int checkmountid)
+{
+       int ret;
+       int mntid_short;
+
+       uint64_t mntid_unique;
+       uint64_t statx_mntid_short = 0, statx_mntid_unique = 0;
+       struct handle dummy_fh;
+
+       if (checkmountid) {
+               struct statx statxbuf;
+
+               /* Get both the short and unique mount id. */
+               if (statx(AT_FDCWD, fname, 0, STATX_MNT_ID, &statxbuf) < 0) {
+                       fprintf(stderr, "%s: statx(STATX_MNT_ID): %m\n", fname);
+                       return EXIT_FAILURE;
+               }
+               if (!(statxbuf.stx_mask & STATX_MNT_ID)) {
+                       fprintf(stderr, "%s: no STATX_MNT_ID in stx_mask\n", fname);
+                       return EXIT_FAILURE;
+               }
+               statx_mntid_short = statxbuf.stx_mnt_id;
+
+               if (statx(AT_FDCWD, fname, 0, STATX_MNT_ID_UNIQUE, &statxbuf) < 0) {
+                       fprintf(stderr, "%s: statx(STATX_MNT_ID_UNIQUE): %m\n", fname);
+                       return EXIT_FAILURE;

+       }
+
+       return 0;
+}
+
 int main(int argc, char **argv)
 {
        int     i, c;

@@ -132,19 +213,20 @@ int main(int argc, char **argv)
        char    fname2[PATH_MAX];
        char    *test_dir;
        char    *mount_dir;
-       int     mount_fd, mount_id;
+       int     mount_fd;
        char    *infile = NULL, *outfile = NULL;
        int     in_fd = 0, out_fd = 0;
        int     numfiles = 1;
        int     create = 0, delete = 0, nlink = 1, move = 0;
        int     rd = 0, wr = 0, wrafter = 0, parent = 0;
        int     keepopen = 0, drop_caches = 1, sleep_loop = 0;
+       int     checkmountid = 0;
        int     bufsz = MAX_HANDLE_SZ;

        if (argc < 2)
                usage();

-       while ((c = getopt(argc, argv, "cludmrwapknhi:o:sz")) != -1) {
+       while ((c = getopt(argc, argv, "cludMmrwapknhi:o:sz")) != -1) {
                switch (c) {
                case 'c':
                        create = 1;

@@ -172,6 +254,9 @@ int main(int argc, char **argv)
                        delete = 1;
                        nlink = 0;
                        break;
+               case 'M':
+                       checkmountid = 1;
+                       break;
                case 'm':
                        move = 1;
                        break;

@@ -307,21 +392,9 @@ int main(int argc, char **argv)
                                return EXIT_FAILURE;
                        }
                } else {
-                       handle[i].fh.handle_bytes = bufsz;
-                       ret = name_to_handle_at(AT_FDCWD, fname, &handle[i].fh, &mount_id, 0);
-                       if (bufsz < handle[i].fh.handle_bytes) {
-                               /* Query the filesystem required bufsz and the file handle */
-                               if (ret != -1 || errno != EOVERFLOW) {
-                                       fprintf(stderr, "Unexpected result from name_to_handle_at(%s)\n", fname);
-                                       return EXIT_FAILURE;
-                               }
-                               ret = name_to_handle_at(AT_FDCWD, fname, &handle[i].fh, &mount_id, 0);
-                       }
-                       if (ret < 0) {
-                               strcat(fname, ": name_to_handle");
-                               perror(fname);
+                       ret = do_name_to_handle_at(fname, &handle[i].fh, bufsz, checkmountid);
+                       if (ret < 0)
                                return EXIT_FAILURE;
-                       }
                }
                if (keepopen) {
                        /* Open without close to keep unlinked files around */

@@ -349,21 +422,9 @@ int main(int argc, char **argv)
                                return EXIT_FAILURE;
                        }
                } else {
-                       dir_handle.fh.handle_bytes = bufsz;
-                       ret = name_to_handle_at(AT_FDCWD, test_dir, &dir_handle.fh, &mount_id, 0);
-                       if (bufsz < dir_handle.fh.handle_bytes) {
-                               /* Query the filesystem required bufsz and the file handle */
-                               if (ret != -1 || errno != EOVERFLOW) {
-                                       fprintf(stderr, "Unexpected result from name_to_handle_at(%s)\n", dname);
-                                       return EXIT_FAILURE;
-                               }
-                               ret = name_to_handle_at(AT_FDCWD, test_dir, &dir_handle.fh, &mount_id, 0);
-                       }
-                       if (ret < 0) {
-                               strcat(dname, ": name_to_handle");
-                               perror(dname);
+                       ret = do_name_to_handle_at(test_dir, &dir_handle.fh, bufsz, checkmountid);
+                       if (ret < 0)
                                return EXIT_FAILURE;
-                       }
                }
                if (out_fd) {
                        ret = write(out_fd, (char *)&dir_handle, sizeof(*handle));

diff --git a/tests/generic/426 b/tests/generic/426
index 25909f220e1e..df481c58562c 100755
--- a/tests/generic/426
+++ b/tests/generic/426

@@ -51,6 +51,7 @@ test_file_handles $testdir -d
 # Check non-stale handles to linked files
 create_test_files $testdir
 test_file_handles $testdir
+test_file_handles $testdir -M