libmount: add helper to log mount messages as emitted by kernel

The kernel helpfully provides feedback about failed operations via the
filesystem descriptor. Read that information and expose it via libmounts
debug facilities.

Signed-off-by: Thomas Weißschuh <thomas@t-8ch.de>

diff --git a/libmount/src/hook_mount.c b/libmount/src/hook_mount.c
index 4b2a534f74e280e0dab27acf6cb80bab25634500..2e0b5f0facade4820b1c714b3ba32319f13c19e2 100644 (file)
--- a/libmount/src/hook_mount.c
+++ b/libmount/src/hook_mount.c
@@ -64,6 +64,31 @@ static void close_sysapi_fds(struct libmnt_sysapi *api)
        api->fd_tree = api->fd_fs = -1;
 }
 
+static void debug_fs_fd_messages(int fd)
+{
+       uint8_t buf[BUFSIZ];
+       int rc;
+
+       while ((rc = read(fd, buf, sizeof(buf))) != -1) {
+               if (rc > 0 && buf[rc - 1] == '\n')
+                       buf[rc - 1] = '\0';
+               DBG(CXT, ul_debug("message from kernel: %*s", rc, buf));
+       }
+}
+
+static void set_syscall_status_cxt_log(struct libmnt_context *cxt,
+                                      const char *name, int x)
+{
+       struct libmnt_sysapi *api;
+
+       set_syscall_status(cxt, name, x);
+
+       if (!x) {
+               api = get_sysapi(cxt);
+               debug_fs_fd_messages(api->fd_fs);
+       }
+}
+
 /*
  * This hookset uses 'struct libmnt_sysapi' (mountP.h) as hookset data.
  */