Re: [PATCH v4 15/16] samples: Add fs error monitoring example

On Tue, Jul 20, 2021 at 7:00 PM Gabriel Krisman Bertazi
[off-list ref] wrote:

Introduce an example of a FAN_FS_ERROR fanotify user to track filesystem
errors.

Signed-off-by: Gabriel Krisman Bertazi <redacted>

Reviewed-by: Amir Goldstein <amir73il@gmail.com>

except for one small nit

If you install the kernel uapi header and try to build this
sample it will fail because FAN_FS_ERROR will be
defined but FILEID_INO32_GEN and FILEID_INVALID
will not be defined.

Thanks,
Amir.

+
+struct fanotify_event_info_error {
+       struct fanotify_event_info_header hdr;
+       __s32 error;
+       __u32 error_count;
+};
+#endif
+
+static void print_fh(struct file_handle *fh)
+{
+       int i;
+       uint32_t *h = (uint32_t *) fh->f_handle;
+
+       printf("\tfh: ");
+       for (i = 0; i < fh->handle_bytes; i++)
+               printf("%hhx", fh->f_handle[i]);
+       printf("\n");
+
+       printf("\tdecoded fh: ");
+       if (fh->handle_type == FILEID_INO32_GEN)
+               printf("inode=%u gen=%u\n", h[0], h[1]);
+       else if (fh->handle_type == FILEID_INVALID && !h[0] && !h[1])
+               printf("Type %d (Superblock error)\n", fh->handle_type);
+       else
+               printf("Type %d (Unknown)\n", fh->handle_type);
+
+}
+
+static void handle_notifications(char *buffer, int len)
+{
+       struct fanotify_event_metadata *metadata;
+       struct fanotify_event_info_error *error;
+       struct fanotify_event_info_fid *fid;
+       char *next;
+
+       for (metadata = (struct fanotify_event_metadata *) buffer;
+            FAN_EVENT_OK(metadata, len);
+            metadata = FAN_EVENT_NEXT(metadata, len)) {
+               next = (char *)metadata + metadata->event_len;
+               if (metadata->mask != FAN_FS_ERROR) {
+                       printf("unexpected FAN MARK: %llx\n", metadata->mask);
+                       goto next_event;
+               } else if (metadata->fd != FAN_NOFD) {
+                       printf("Unexpected fd (!= FAN_NOFD)\n");
+                       goto next_event;
+               }
+
+               printf("FAN_FS_ERROR found len=%d\n", metadata->event_len);
+
+               error = (struct fanotify_event_info_error *) (metadata+1);
+               if (error->hdr.info_type != FAN_EVENT_INFO_TYPE_ERROR) {
+                       printf("unknown record: %d (Expecting TYPE_ERROR)\n",
+                              error->hdr.info_type);
+                       goto next_event;
+               }
+
+               printf("\tGeneric Error Record: len=%d\n", error->hdr.len);
+               printf("\terror: %d\n", error->error);
+               printf("\terror_count: %d\n", error->error_count);
+
+               fid = (struct fanotify_event_info_fid *) (error + 1);
+               if ((char *) fid >= next) {
+                       printf("Event doesn't have FID\n");
+                       goto next_event;
+               }
+               printf("FID record found\n");
+
+               if (fid->hdr.info_type != FAN_EVENT_INFO_TYPE_FID) {
+                       printf("unknown record: %d (Expecting TYPE_FID)\n",
+                              fid->hdr.info_type);
+                       goto next_event;
+               }
+               printf("\tfsid: %x%x\n", fid->fsid.val[0], fid->fsid.val[1]);
+               print_fh((struct file_handle *) &fid->handle);
+
+next_event:
+               printf("---\n\n");
+       }
+}
+
+int main(int argc, char **argv)
+{
+       int fd;
+
+       char buffer[BUFSIZ];
+
+       if (argc < 2) {
+               printf("Missing path argument\n");
+               return 1;
+       }
+
+       fd = fanotify_init(FAN_CLASS_NOTIF|FAN_REPORT_FID, O_RDONLY);
+       if (fd < 0)
+               errx(1, "fanotify_init");
+
+       if (fanotify_mark(fd, FAN_MARK_ADD|FAN_MARK_FILESYSTEM,
+                         FAN_FS_ERROR, AT_FDCWD, argv[1])) {
+               errx(1, "fanotify_mark");
+       }
+
+       while (1) {
+               int n = read(fd, buffer, BUFSIZ);
+
+               if (n < 0)
+                       errx(1, "read");
+
+               handle_notifications(buffer, n);
+       }
+
+       return 0;
+}
--
2.32.0