[Libguestfs] [PATCH] New API: part_expand_gpt.

[Maxim Perevedentsev]

This action moves second(backup) GPT header to the end of the disk.
It is usable in in-place image expanding, since free space after
second GPT header is unusable. To use additional space, we have
to move second header. This is what sgdisk -e does.

However, sgdisk -e may perform additional actions if the partition
table has unexpected params (e.g. if we call sgdisk -e /dev/sda1,
it may fix partition table thus destroying the filesystem).
To prevent such cases, we do a dry-run at first and fail if
additional actions are scheduled.
---
 daemon/parted.c      | 33 +++++++++++++++++++++++++++++++++
 generator/actions.ml | 14 ++++++++++++++
 src/MAX_PROC_NR      |  2 +-
 3 files changed, 48 insertions(+), 1 deletion(-)

diff --git a/daemon/parted.c b/daemon/parted.c
index df6b7e7..033c136 100644
--- a/daemon/parted.c
+++ b/daemon/parted.c
@@ -928,3 +928,36 @@ do_part_get_mbr_part_type (const char *device, int partnum)
   reply_with_error ("strdup failed");
   return NULL;
 }
+
+int
+do_part_expand_gpt(const char *device)
+{
+  CLEANUP_FREE char *err = NULL;
+
+  /* If something is broken, sgdisk may try to correct it.
+   * (e.g. recreate partition table and so on).
+   * We do not want such behavior, so dry-run at first.*/
+  int r = commandf (NULL, &err, COMMAND_FLAG_FOLD_STDOUT_ON_STDERR,
+                    str_sgdisk, "--pretend", "-e", device, NULL);
+
+  if (r == -1) {
+    reply_with_error ("%s --pretend -e %s: %s", str_sgdisk, device, err);
+    return -1;
+  }
+  if (err && strlen(err) != 0) {
+    /* Unexpected actions. */
+    reply_with_error ("%s --pretend -e %s: %s", str_sgdisk, device, err);
+    return -1;
+  }
+
+  /* Now we can do a real run. */
+  r = commandf (NULL, &err, COMMAND_FLAG_FOLD_STDOUT_ON_STDERR,
+                str_sgdisk, "-e", device, NULL);
+
+  if (r == -1) {
+    reply_with_error ("%s -e %s: %s", str_sgdisk, device, err);
+    return -1;
+  }
+
+  return 0;
+}
diff --git a/generator/actions.ml b/generator/actions.ml
index 7ab8ee4..3a14683 100644
--- a/generator/actions.ml
+++ b/generator/actions.ml
@@ -12787,6 +12787,20 @@ See also L<ntfsresize(8)>, L<resize2fs(8)>, L<btrfs(8)>, L<xfs_info(8)>." };
     longdesc = "\
 This is the internal call which implements C<guestfs_feature_available>." };
 
+  { defaults with
+    name = "part_expand_gpt"; added = (1, 31, 29);
+    style = RErr, [Device "device"], [];
+    proc_nr = Some 459;
+    optional = Some "gdisk";
+    shortdesc = "move backup GPT header to the end of the disk";
+    longdesc = "\
+Move backup GPT data structures to the end of the disk.
+This is useful in case of in-place image expand
+since disk space after backup GPT header is not usable.
+This is equivalent to C<sgdisk -e>.
+
+See also L<sgdisk(8)>." };
+
 ]
 
 (* Non-API meta-commands available only in guestfish.
diff --git a/src/MAX_PROC_NR b/src/MAX_PROC_NR
index c92ddb6..658bd78 100644
--- a/src/MAX_PROC_NR
+++ b/src/MAX_PROC_NR
@@ -1 +1 @@
-458
+459
-- 
1.8.3.1