Re: [Libguestfs] [PATCH] appliance: extract UUID from QCOW2 disk image

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(a)openvz.org&gt; >Signed-off-by: Andrey Shinkevich <andrey.shinkevich(a)virtuozzo.com&gt; >--- > 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.

>+ } >+ >+ 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