[Libguestfs] [PATCH] daemon: use btrfs(1) to get btrfs labels

[Pino Toscano]

blkid(1) (or actually, libblkid) seems to handle file system labels up
to 127 characters. Considering that btrfs labels can be up to 255
characters, this means long labels are not read correctly (i.e. get
truncated) by blkid.

Get the file system type, and if btrfs is available invoke
`btrfs filesystem` to get the label of btrfs file systems.
---
 daemon/blkid.c  |  6 ++++++
 daemon/btrfs.c  | 24 ++++++++++++++++++++++++
 daemon/daemon.h |  3 +++
 3 files changed, 33 insertions(+)

diff --git a/daemon/blkid.c b/daemon/blkid.c
index b98c155..2c9e2f1 100644
--- a/daemon/blkid.c
+++ b/daemon/blkid.c
@@ -26,6 +26,7 @@
 
 #include "daemon.h"
 #include "actions.h"
+#include "optgroups.h"
 
 GUESTFSD_EXT_CMD(str_blkid, blkid);
 
@@ -76,6 +77,11 @@ do_vfs_type (const mountable_t *mountable)
 char *
 do_vfs_label (const mountable_t *mountable)
 {
+  CLEANUP_FREE char *type = do_vfs_type (mountable);
+
+  if (type && STREQ (type, "btrfs") && optgroup_btrfs_available ())
+    return btrfs_get_label (mountable->device);
+
   return get_blkid_tag (mountable->device, "LABEL");
 }
 
diff --git a/daemon/btrfs.c b/daemon/btrfs.c
index 150c089..cf1507d 100644
--- a/daemon/btrfs.c
+++ b/daemon/btrfs.c
@@ -44,6 +44,30 @@ optgroup_btrfs_available (void)
   return prog_exists (str_btrfs) && filesystem_available ("btrfs") > 0;
 }
 
+char *
+btrfs_get_label (const char *device)
+{
+  int r;
+  CLEANUP_FREE char *err = NULL;
+  char *out = NULL;
+  size_t len;
+
+  r = command (&out, &err, str_btrfs, "filesystem", "label",
+               device, NULL);
+  if (r == -1) {
+    reply_with_error ("%s", err);
+    free (out);
+    return NULL;
+  }
+
+  /* Trim trailing \n if present. */
+  len = strlen (out);
+  if (len > 0 && out[len-1] == '\n')
+    out[len-1] = '\0';
+
+  return out;
+}
+
 /* Takes optional arguments, consult optargs_bitmask. */
 int
 do_btrfs_filesystem_resize (const char *filesystem, int64_t size)
diff --git a/daemon/daemon.h b/daemon/daemon.h
index c101c3b..cf123bf 100644
--- a/daemon/daemon.h
+++ b/daemon/daemon.h
@@ -232,6 +232,9 @@ extern void wipe_device_before_mkfs (const char *device);
 extern void aug_read_version (void);
 extern void aug_finalize (void);
 
+/*-- in btrfs.c --*/
+extern char *btrfs_get_label (const char *device);
+
 /* The version of augeas, saved as:
  * (MAJOR << 16) | (MINOR << 8) | PATCH
  */
-- 
1.9.3