[Libguestfs] [PATCH] appliance: extract UUID from QCOW2 disk image
Richard W.M. Jones
rjones at redhat.com
Wed Aug 12 13:25:46 UTC 2020
On Wed, Aug 12, 2020 at 03:52:34PM +0300, Vladimir Sementsov-Ogievskiy wrote:
> 12.08.2020 15:39, Andrey Shinkevich wrote:
> >For the appliance of the QCOW2 format, get the UUID of the disk by
> >reading the first 256k bytes with 'qemu-img dd' command. Then pass the
> >read block to the 'file' command. In case of failure, run the 'file'
> >command again directly.
> >
> >Suggested-by: Denis V. Lunev <den at openvz.org>
> >Signed-off-by: Andrey Shinkevich <andrey.shinkevich at virtuozzo.com>
> >---
> > lib/appliance-kcmdline.c | 70 +++++++++++++++++++++++++++++++++++++++++++++++-
> > 1 file changed, 69 insertions(+), 1 deletion(-)
> >
> >diff --git a/lib/appliance-kcmdline.c b/lib/appliance-kcmdline.c
> >index 211cc46..3bb8bcd 100644
> >--- a/lib/appliance-kcmdline.c
> >+++ b/lib/appliance-kcmdline.c
> >@@ -71,7 +71,7 @@ read_uuid (guestfs_h *g, void *retv, const char *line, size_t len)
> > * The L<file(1)> command does the hard work.
> > */
> > static char *
> >-get_root_uuid (guestfs_h *g, const char *appliance)
> >+do_get_root_uuid (guestfs_h *g, const char *appliance)
> > {
> > CLEANUP_CMD_CLOSE struct command *cmd = guestfs_int_new_command (g);
> > char *ret = NULL;
> >@@ -96,6 +96,74 @@ get_root_uuid (guestfs_h *g, const char *appliance)
> > }
> > /**
> >+ * Read the first 256k bytes of the in_file with L<qemu-img(1)> command
> >+ * and write them into the out_file. That may be useful to get UUID of
> >+ * the QCOW2 disk image with further L<file(1)> command.
> >+ * The function returns zero if successful, otherwise -1.
> >+ */
> >+static int
> >+run_qemu_img_dd (guestfs_h *g, const char *in_file, char *out_file)
> >+{
> >+ CLEANUP_CMD_CLOSE struct command *cmd = guestfs_int_new_command (g);
> >+ int r;
> >+
> >+ guestfs_int_cmd_add_arg (cmd, "qemu-img");
> >+ guestfs_int_cmd_add_arg (cmd, "dd");
> >+ guestfs_int_cmd_add_arg_format (cmd, "if=%s", in_file);
> >+ guestfs_int_cmd_add_arg_format (cmd, "of=%s", out_file);
> >+ guestfs_int_cmd_add_arg (cmd, "bs=256k");
> >+ guestfs_int_cmd_add_arg (cmd, "count=1");
> >+
> >+ r = guestfs_int_cmd_run (cmd);
> >+ if (r == -1) {
> >+ error (g, "Failed to run qemu-img");
> >+ return -1;
> >+ }
> >+ if (!WIFEXITED (r) || WEXITSTATUS (r) != 0) {
> >+ guestfs_int_external_command_failed (g, r, "qemu-img dd", NULL);
> >+ return -1;
> >+ }
> >+
> >+ return 0;
> >+}
> >+
> >+/**
> >+ * Get the UUID from the appliance disk image.
> >+ */
> >+static char *
> >+get_root_uuid (guestfs_h *g, const char *appliance)
> >+{
> >+ char *UUID = NULL;
>
> Generally, don't use uppercase for local variables, I'd rename it s/UUID/uuid/
>
> >+ int ret;
> >+ char tmp_file[] = "/tmp/libguestfsXXXXXX";
> >+
> >+ if (!mktemp (tmp_file)) {
> >+ error (g, "get_root_uuid: mktemp failed");
> >+ return NULL;
>
> Hmm, if failed to create temp file, we still can try call do_get_root_uuid on original appliance image.
This is related to the only issue I had with this patch. Can
we run the find command first on the original appliance, and only
if it fails take the slower qemu-img dd patch?
I tested this patch as it is, and it worked for me.
Rich.
> >+ }
> >+
> >+ ret = run_qemu_img_dd (g, appliance, tmp_file);
> >+ if (ret == 0) {
> >+ UUID = do_get_root_uuid (g, tmp_file);
> >+ if (UUID) {
> >+ goto out;
> >+ }
> >+ }
> >+
> >+ /* We get here in case of failure to extract a UUID from the temporary file.
> >+ * Let us try to get the UUID from the appliance directly.
> >+ */
> >+ UUID = do_get_root_uuid (g, appliance);
> >+ if (!UUID) {
> >+ error (g, "Failed to get the appliance UUID");
> >+ }
> >+
> >+out:
> >+ unlink (tmp_file);
> >+ return UUID;
> >+}
> >+
> >+/**
> > * Construct the Linux command line passed to the appliance. This is
> > * used by the C<direct> and C<libvirt> backends, and is simply
> > * located in this file because it's a convenient place for this
> >
>
>
> --
> Best regards,
> Vladimir
--
Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones
Read my programming and virtualization blog: http://rwmj.wordpress.com
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