libguestfs/daemon/parted.c

/* libguestfs - the guestfsd daemon
 * Copyright (C) 2009-2015 Red Hat Inc.
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
 */

#include <config.h>

#include <stdio.h>
#include <stdlib.h>
#include <stdint.h>
#include <inttypes.h>
#include <string.h>
#include <unistd.h>

#include "daemon.h"
#include "actions.h"
#include "optgroups.h"

GUESTFSD_EXT_CMD(str_parted, parted);
GUESTFSD_EXT_CMD(str_sfdisk, sfdisk);
GUESTFSD_EXT_CMD(str_sgdisk, sgdisk);

/* Notes:
 *
 * Parted 1.9 sends error messages to stdout, hence use of the
 * COMMAND_FLAG_FOLD_STDOUT_ON_STDERR flag.
 *
 * There is a reason why we call udev_settle both before and after
 * each command.  When you call close on any block device, udev kicks
 * off a rule which runs blkid to reexamine the device.  We need to
 * wait for this rule to finish running (from a previous operation)
 * since it holds the device open.  Since parted also closes the block
 * device, it can cause udev to run again, hence the call to
 * udev_settle afterwards.
 */

static const char *
check_parttype (const char *parttype)
{
  /* Check and translate parttype. */
  if (STREQ (parttype, "aix") ||
      STREQ (parttype, "amiga") ||
      STREQ (parttype, "bsd") ||
      STREQ (parttype, "dasd") ||
      STREQ (parttype, "dvh") ||
      STREQ (parttype, "gpt") ||
      STREQ (parttype, "mac") ||
      STREQ (parttype, "msdos") ||
      STREQ (parttype, "pc98") ||
      STREQ (parttype, "sun"))
    return parttype;
  else if (STREQ (parttype, "rdb"))
    return "amiga";
  else if (STREQ (parttype, "efi"))
    return "gpt";
  else if (STREQ (parttype, "mbr"))
    return "msdos";
  else
    return NULL;
}

int
do_part_init (const char *device, const char *parttype)
{
  int r;
  CLEANUP_FREE char *err = NULL;

  parttype = check_parttype (parttype);
  if (!parttype) {
    reply_with_error ("unknown partition type: common choices are \"gpt\" and \"msdos\"");
    return -1;
  }

  udev_settle ();

  r = commandf (NULL, &err, COMMAND_FLAG_FOLD_STDOUT_ON_STDERR,
                str_parted, "-s", "--", device, "mklabel", parttype, NULL);
  if (r == -1) {
    reply_with_error ("parted: %s: %s", device, err);
    return -1;
  }

  udev_settle ();

  return 0;
}

int
do_part_add (const char *device, const char *prlogex,
             int64_t startsect, int64_t endsect)
{
  int r;
  CLEANUP_FREE char *err = NULL;
  char startstr[32];
  char endstr[32];

  /* Check and translate prlogex. */
  if (STREQ (prlogex, "primary") ||
      STREQ (prlogex, "logical") ||
      STREQ (prlogex, "extended"))
    ;
  else if (STREQ (prlogex, "p"))
    prlogex = "primary";
  else if (STREQ (prlogex, "l"))
    prlogex = "logical";
  else if (STREQ (prlogex, "e"))
    prlogex = "extended";
  else {
    reply_with_error ("unknown partition type: %s: this should be \"primary\", \"logical\" or \"extended\"", prlogex);
    return -1;
  }

  if (startsect < 0) {
    reply_with_error ("startsect cannot be negative");
    return -1;
  }
  /* but endsect can be negative */

  snprintf (startstr, sizeof startstr, "%" PRIi64 "s", startsect);
  snprintf (endstr, sizeof endstr, "%" PRIi64 "s", endsect);

  udev_settle ();

  /* XXX Bug: If the partition table type (which we don't know in this
   * function) is GPT, then this parted command sets the _partition
   * name_ to prlogex, eg. "primary".  I would essentially describe
   * this as a bug in the parted mkpart command.
   */
  r = commandf (NULL, &err, COMMAND_FLAG_FOLD_STDOUT_ON_STDERR,
                str_parted, "-s", "--",
                device, "mkpart", prlogex, startstr, endstr, NULL);
  if (r == -1) {
    reply_with_error ("parted: %s: %s", device, err);
    return -1;
  }

  udev_settle ();

  return 0;
}

int
do_part_del (const char *device, int partnum)
{
  int r;
  CLEANUP_FREE char *err = NULL;

  if (partnum <= 0) {
    reply_with_error ("partition number must be >= 1");
    return -1;
  }

  char partnum_str[16];
  snprintf (partnum_str, sizeof partnum_str, "%d", partnum);

  udev_settle ();

  r = commandf (NULL, &err, COMMAND_FLAG_FOLD_STDOUT_ON_STDERR,
                str_parted, "-s", "--", device, "rm", partnum_str, NULL);
  if (r == -1) {
    reply_with_error ("parted: %s: %s", device, err);
    return -1;
  }

  udev_settle ();

  return 0;
}

int
do_part_disk (const char *device, const char *parttype)
{
  int r;
  CLEANUP_FREE char *err = NULL;

  parttype = check_parttype (parttype);
  if (!parttype) {
    reply_with_error ("unknown partition type: common choices are \"gpt\" and \"msdos\"");
    return -1;
  }

  /* Align all partitions created this way to 128 sectors, and leave
   * the last 128 sectors at the end of the disk free.  This wastes
   * 64K+64K = 128K on 512-byte sector disks.  The rationale is:
   *
   * - aligned operations are faster
   * - absolute minimum recommended alignment is 64K (1M would be better)
   * - GPT requires at least 34 sectors* at the end of the disk.
   *
   *   *=except for 4k sector disks, where only 6 sectors are required
   */
  const char *startstr = "128s";
  const char *endstr = "-128s";

  udev_settle ();

  r = commandf (NULL, &err, COMMAND_FLAG_FOLD_STDOUT_ON_STDERR,
                str_parted, "-s", "--",
                device,
                "mklabel", parttype,
                /* See comment about about the parted mkpart command. */
                "mkpart", STREQ (parttype, "gpt") ? "p1" : "primary",
                startstr, endstr, NULL);
  if (r == -1) {
    reply_with_error ("parted: %s: %s", device, err);
    return -1;
  }

  udev_settle ();

  return 0;
}

int
do_part_set_bootable (const char *device, int partnum, int bootable)
{
  int r;
  CLEANUP_FREE char *err = NULL;

  if (partnum <= 0) {
    reply_with_error ("partition number must be >= 1");
    return -1;
  }

  char partstr[16];

  snprintf (partstr, sizeof partstr, "%d", partnum);

  udev_settle ();

  r = commandf (NULL, &err, COMMAND_FLAG_FOLD_STDOUT_ON_STDERR,
                str_parted, "-s", "--",
                device, "set", partstr, "boot", bootable ? "on" : "off", NULL);
  if (r == -1) {
    reply_with_error ("parted: %s: %s", device, err);
    return -1;
  }

  udev_settle ();

  return 0;
}

int
do_part_set_name (const char *device, int partnum, const char *name)
{
  int r;
  CLEANUP_FREE char *err = NULL;

  if (partnum <= 0) {
    reply_with_error ("partition number must be >= 1");
    return -1;
  }

  char partstr[16];

  snprintf (partstr, sizeof partstr, "%d", partnum);

  udev_settle ();

  r = commandf (NULL, &err, COMMAND_FLAG_FOLD_STDOUT_ON_STDERR,
                str_parted, "-s", "--", device, "name", partstr, name, NULL);
  if (r == -1) {
    reply_with_error ("parted: %s: %s", device, err);
    return -1;
  }

  udev_settle ();

  return 0;
}

/* Return the nth field from a string of ':'/';'-delimited strings.
 * Useful for parsing the return value from 'parted -m'.
 */
static char *
get_table_field (const char *line, int n)
{
  const char *p = line;

  while (*p && n > 0) {
    p += strcspn (p, ":;") + 1;
    n--;
  }

  if (n > 0) {
    reply_with_error ("not enough fields in output of parted print command: %s",
                      line);
    return NULL;
  }

  size_t len = strcspn (p, ":;");
  char *q = strndup (p, len);
  if (q == NULL) {
    reply_with_perror ("strndup");
    return NULL;
  }

  return q;
}

/* RHEL 5 parted doesn't have the -m (machine readable) option so we
 * must do a lot more work to parse the output in
 * print_partition_table below.  Test for this option the first time
 * this function is called.
 */
static int
test_parted_m_opt (void)
{
  static int result = -1;

  if (result >= 0)
    return result;

  CLEANUP_FREE char *err = NULL;
  int r = commandr (NULL, &err, str_parted, "-s", "-m", "/dev/null", NULL);
  if (r == -1) {
    /* Test failed, eg. missing or completely unusable parted binary. */
    reply_with_error ("could not run 'parted' command");
    return -1;
  }

  if (err && strstr (err, "invalid option -- m"))
    result = 0;
  else
    result = 1;
  return result;
}

static char *
print_partition_table (const char *device, int parted_has_m_opt)
{
  char *out;
  CLEANUP_FREE char *err = NULL;
  int r;

  if (parted_has_m_opt)
    r = command (&out, &err, str_parted, "-m", "--", device,
                 "unit", "b",
                 "print", NULL);
  else
    r = command (&out, &err, str_parted, "-s", "--", device,
                 "unit", "b",
                 "print", NULL);
  if (r == -1) {
    reply_with_error ("parted print: %s: %s", device,
                      /* Hack for parted 1.x which sends errors to stdout. */
                      *err ? err : out);
    free (out);
    return NULL;
  }

  return out;
}

char *
do_part_get_parttype (const char *device)
{
  int parted_has_m_opt = test_parted_m_opt ();
  if (parted_has_m_opt == -1)
    return NULL;

  CLEANUP_FREE char *out = print_partition_table (device, parted_has_m_opt);
  if (!out)
    return NULL;

  if (parted_has_m_opt) {
    /* New-style parsing using the "machine-readable" format from
     * 'parted -m'.
     */
    CLEANUP_FREE_STRING_LIST char **lines = split_lines (out);

    if (!lines)
      return NULL;

    if (lines[0] == NULL || STRNEQ (lines[0], "BYT;")) {
      reply_with_error ("unknown signature, expected \"BYT;\" as first line of the output: %s",
                        lines[0] ? lines[0] : "(signature was null)");
      return NULL;
    }

    if (lines[1] == NULL) {
      reply_with_error ("parted didn't return a line describing the device");
      return NULL;
    }

    /* lines[1] is something like:
     * "/dev/sda:1953525168s:scsi:512:512:msdos:ATA Hitachi HDT72101;"
     */
    char *r = get_table_field (lines[1], 5);
    if (r == NULL) {
      return NULL;
    }

    /* If "loop" return an error (RHBZ#634246). */
    if (STREQ (r, "loop")) {
      free (r);
      reply_with_error ("not a partitioned device");
      return NULL;
    }

    return r;
  }
  else {
    /* Old-style.  Look for "\nPartition Table: <str>\n". */
    char *p = strstr (out, "\nPartition Table: ");
    if (!p) {
      reply_with_error ("parted didn't return Partition Table line");
      return NULL;
    }

    p += 18;
    char *q = strchr (p, '\n');
    if (!q) {
      reply_with_error ("parted Partition Table has no end of line char");
      return NULL;
    }

    *q = '\0';

    p = strdup (p);
    if (!p) {
      reply_with_perror ("strdup");
      return NULL;
    }

    /* If "loop" return an error (RHBZ#634246). */
    if (STREQ (p, "loop")) {
      free (p);
      reply_with_error ("not a partitioned device");
      return NULL;
    }

    return p;                   /* caller frees */
  }
}

guestfs_int_partition_list *
do_part_list (const char *device)
{
  int parted_has_m_opt = test_parted_m_opt ();
  if (parted_has_m_opt == -1)
    return NULL;

  CLEANUP_FREE char *out = print_partition_table (device, parted_has_m_opt);
  if (!out)
    return NULL;

  CLEANUP_FREE_STRING_LIST char **lines = split_lines (out);

  if (!lines)
    return NULL;

  guestfs_int_partition_list *r;

  if (parted_has_m_opt) {
    /* New-style parsing using the "machine-readable" format from
     * 'parted -m'.
     *
     * lines[0] is "BYT;", lines[1] is the device line which we ignore,
     * lines[2..] are the partitions themselves.  Count how many.
     */
    size_t nr_rows = 0, row;
    for (row = 2; lines[row] != NULL; ++row)
      ++nr_rows;

    r = malloc (sizeof *r);
    if (r == NULL) {
      reply_with_perror ("malloc");
      return NULL;
    }
    r->guestfs_int_partition_list_len = nr_rows;
    r->guestfs_int_partition_list_val =
      malloc (nr_rows * sizeof (guestfs_int_partition));
    if (r->guestfs_int_partition_list_val == NULL) {
      reply_with_perror ("malloc");
      goto error2;
    }

    /* Now parse the lines. */
    size_t i;
    for (i = 0, row = 2; lines[row] != NULL; ++i, ++row) {
      if (sscanf (lines[row], "%d:%" SCNi64 "B:%" SCNi64 "B:%" SCNi64 "B",
                  &r->guestfs_int_partition_list_val[i].part_num,
                  &r->guestfs_int_partition_list_val[i].part_start,
                  &r->guestfs_int_partition_list_val[i].part_end,
                  &r->guestfs_int_partition_list_val[i].part_size) != 4) {
        reply_with_error ("could not parse row from output of parted print command: %s", lines[row]);
        goto error3;
      }
    }
  }
  else {
    /* Old-style.  Start at the line following "^Number", up to the
     * next blank line.
     */
    size_t start = 0, end = 0, row;

    for (row = 0; lines[row] != NULL; ++row)
      if (STRPREFIX (lines[row], "Number")) {
        start = row+1;
        break;
      }

    if (start == 0) {
      reply_with_error ("parted output has no \"Number\" line");
      return NULL;
    }

    for (row = start; lines[row] != NULL; ++row)
      if (STREQ (lines[row], "")) {
        end = row;
        break;
      }

    if (end == 0) {
      reply_with_error ("parted output has no blank after end of table");
      return NULL;
    }

    size_t nr_rows = end - start;

    r = malloc (sizeof *r);
    if (r == NULL) {
      reply_with_perror ("malloc");
      return NULL;
    }
    r->guestfs_int_partition_list_len = nr_rows;
    r->guestfs_int_partition_list_val =
      malloc (nr_rows * sizeof (guestfs_int_partition));
    if (r->guestfs_int_partition_list_val == NULL) {
      reply_with_perror ("malloc");
      goto error2;
    }

    /* Now parse the lines. */
    size_t i;
    for (i = 0, row = start; row < end; ++i, ++row) {
      if (sscanf (lines[row], " %d %" SCNi64 "B %" SCNi64 "B %" SCNi64 "B",
                  &r->guestfs_int_partition_list_val[i].part_num,
                  &r->guestfs_int_partition_list_val[i].part_start,
                  &r->guestfs_int_partition_list_val[i].part_end,
                  &r->guestfs_int_partition_list_val[i].part_size) != 4) {
        reply_with_error ("could not parse row from output of parted print command: %s", lines[row]);
        goto error3;
      }
    }
  }

  return r;

 error3:
  free (r->guestfs_int_partition_list_val);
 error2:
  free (r);
  return NULL;
}

int
do_part_get_bootable (const char *device, int partnum)
{
  if (partnum <= 0) {
    reply_with_error ("partition number must be >= 1");
    return -1;
  }

  int parted_has_m_opt = test_parted_m_opt ();
  if (parted_has_m_opt == -1)
    return -1;

  CLEANUP_FREE char *out = print_partition_table (device, parted_has_m_opt);
  if (!out)
    return -1;

  CLEANUP_FREE_STRING_LIST char **lines = split_lines (out);

  if (!lines)
    return -1;

  if (parted_has_m_opt) {
    /* New-style parsing using the "machine-readable" format from
     * 'parted -m'.
     *
     * Partitions may not be in any order, so we have to look for
     * the matching partition number (RHBZ#602997).
     */
    if (lines[0] == NULL || STRNEQ (lines[0], "BYT;")) {
      reply_with_error ("unknown signature, expected \"BYT;\" as first line of the output: %s",
                        lines[0] ? lines[0] : "(signature was null)");
      return -1;
    }

    if (lines[1] == NULL) {
      reply_with_error ("parted didn't return a line describing the device");
      return -1;
    }

    size_t row;
    int pnum;
    for (row = 2; lines[row] != NULL; ++row) {
      if (sscanf (lines[row], "%d:", &pnum) != 1) {
        reply_with_error ("could not parse row from output of parted print command: %s", lines[row]);
        return -1;
      }
      if (pnum == partnum)
        break;
    }

    if (lines[row] == NULL) {
      reply_with_error ("partition number %d not found", partnum);
      return -1;
    }

    CLEANUP_FREE char *boot = get_table_field (lines[row], 6);
    if (boot == NULL)
      return -1;

    return strstr (boot, "boot") != NULL;
  }
  else {
    /* Old-style: First look for the line matching "^Number". */
    size_t start = 0, header, row;

    for (row = 0; lines[row] != NULL; ++row)
      if (STRPREFIX (lines[row], "Number")) {
        start = row+1;
        header = row;
        break;
      }

    if (start == 0) {
      reply_with_error ("parted output has no \"Number\" line");
      return -1;
    }

    /* Now we have to look at the column number of the "Flags" field.
     * This is because parted's output has no way to represent a
     * missing field except as whitespace, so we cannot just count
     * fields from the left.  eg. The "File system" field is often
     * missing in the output.
     */
    char *p = strstr (lines[header], "Flags");
    if (!p) {
      reply_with_error ("parted output has no \"Flags\" field");
      return -1;
    }
    size_t col = p - lines[header];

    /* Partitions may not be in any order, so we have to look for
     * the matching partition number (RHBZ#602997).
     */
    int pnum;
    for (row = start; lines[row] != NULL; ++row) {
      if (sscanf (lines[row], " %d", &pnum) != 1) {
        reply_with_error ("could not parse row from output of parted print command: %s", lines[row]);
        return -1;
      }
      if (pnum == partnum)
        break;
    }

    if (lines[row] == NULL) {
      reply_with_error ("partition number %d not found", partnum);
      return -1;
    }

    return STRPREFIX (&lines[row][col], "boot");
  }
}

/* Test if sfdisk is recent enough to have --part-type, to be used instead
 * of --print-id and --change-id.
 */
static int
test_sfdisk_has_part_type (void)
{
  static int tested = -1;

  if (tested != -1)
    return tested;

  int r;
  CLEANUP_FREE char *out = NULL, *err = NULL;

  r = command (&out, &err, str_sfdisk, "--help", NULL);
  if (r == -1) {
    reply_with_error ("%s: %s", "sfdisk --help", err);
    return -1;
  }

  tested = strstr (out, "--part-type") != NULL;
  return tested;
}

/* Currently we use sfdisk for getting and setting the ID byte.  In
 * future, extend parted to provide this functionality.  As a result
 * of using sfdisk, this won't work for non-MBR-style partitions, but
 * that limitation is noted in the documentation and we can extend it
 * later without breaking the ABI.
 */
int
do_part_get_mbr_id (const char *device, int partnum)
{
  if (partnum <= 0) {
    reply_with_error ("partition number must be >= 1");
    return -1;
  }

  const char *param = test_sfdisk_has_part_type () ? "--part-type" : "--print-id";

  char partnum_str[16];
  snprintf (partnum_str, sizeof partnum_str, "%d", partnum);

  CLEANUP_FREE char *out = NULL, *err = NULL;
  int r;

  udev_settle ();

  r = command (&out, &err, str_sfdisk, param, device, partnum_str, NULL);
  if (r == -1) {
    reply_with_error ("sfdisk %s: %s", param, err);
    return -1;
  }

  udev_settle ();

  /* It's printed in hex ... */
  int id;
  if (sscanf (out, "%x", &id) != 1) {
    reply_with_error ("sfdisk --print-id: cannot parse output: %s", out);
    return -1;
  }

  return id;
}

int
do_part_set_mbr_id (const char *device, int partnum, int idbyte)
{
  if (partnum <= 0) {
    reply_with_error ("partition number must be >= 1");
    return -1;
  }

  const char *param = test_sfdisk_has_part_type () ? "--part-type" : "--change-id";

  char partnum_str[16];
  snprintf (partnum_str, sizeof partnum_str, "%d", partnum);

  char idbyte_str[16];
  snprintf (idbyte_str, sizeof partnum_str, "%x", idbyte); /* NB: hex */

  CLEANUP_FREE char *err = NULL;
  int r;

  udev_settle ();

  r = command (NULL, &err, str_sfdisk,
               param, device, partnum_str, idbyte_str, NULL);
  if (r == -1) {
    reply_with_error ("sfdisk %s: %s", param, err);
    return -1;
  }

  udev_settle ();

  return 0;
}

int
optgroup_gdisk_available (void)
{
  return prog_exists (str_sgdisk);
}

int
do_part_set_gpt_type (const char *device, int partnum, const char *guid)
{
  if (partnum <= 0) {
    reply_with_error ("partition number must be >= 1");
    return -1;
  }

  CLEANUP_FREE char *typecode = NULL;
  if (asprintf (&typecode, "%i:%s", partnum, guid) == -1) {
    reply_with_perror ("asprintf");
    return -1;
  }

  CLEANUP_FREE char *err = NULL;
  int r = commandf (NULL, &err, COMMAND_FLAG_FOLD_STDOUT_ON_STDERR,
                    str_sgdisk, device, "-t", typecode, NULL);

  if (r == -1) {
    reply_with_error ("%s %s -t %s: %s", str_sgdisk, device, typecode, err);
    return -1;
  }

  return 0;
}

int
do_part_set_gpt_guid (const char *device, int partnum, const char *guid)
{
  if (partnum <= 0) {
    reply_with_error ("partition number must be >= 1");
    return -1;
  }

  CLEANUP_FREE char *typecode = NULL;
  if (asprintf (&typecode, "%i:%s", partnum, guid) == -1) {
    reply_with_perror ("asprintf");
    return -1;
  }

  CLEANUP_FREE char *err = NULL;
  int r = commandf (NULL, &err, COMMAND_FLAG_FOLD_STDOUT_ON_STDERR,
                    str_sgdisk, device, "-u", typecode, NULL);

  if (r == -1) {
    reply_with_error ("%s %s -u %s: %s", str_sgdisk, device, typecode, err);
    return -1;
  }

  return 0;
}

static char *
sgdisk_info_extract_field (const char *device, int partnum, const char *field,
                           char *(*extract) (const char *path))
{
  if (partnum <= 0) {
    reply_with_error ("partition number must be >= 1");
    return NULL;
  }

  CLEANUP_FREE char *partnum_str = NULL;
  if (asprintf (&partnum_str, "%i", partnum) == -1) {
    reply_with_perror ("asprintf");
    return NULL;
  }

  CLEANUP_FREE char *err = NULL;
  int r = commandf (NULL, &err, COMMAND_FLAG_FOLD_STDOUT_ON_STDERR,
                    str_sgdisk, device, "-i", partnum_str, NULL);

  if (r == -1) {
    reply_with_error ("%s %s -i %s: %s", str_sgdisk, device, partnum_str, err);
    return NULL;
  }

  CLEANUP_FREE_STRING_LIST char **lines = split_lines (err);
  if (lines == NULL) {
    reply_with_error ("'%s %s -i %i' returned no output",
                      str_sgdisk, device, partnum);
    return NULL;
  }

  int fieldlen = strlen (field);

  /* Parse the output of sgdisk -i:
   * Partition GUID code: 21686148-6449-6E6F-744E-656564454649 (BIOS boot partition)
   * Partition unique GUID: 19AEC5FE-D63A-4A15-9D37-6FCBFB873DC0
   * First sector: 2048 (at 1024.0 KiB)
   * Last sector: 411647 (at 201.0 MiB)
   * Partition size: 409600 sectors (200.0 MiB)
   * Attribute flags: 0000000000000000
   * Partition name: 'EFI System Partition'
   */
  for (char **i = lines; *i != NULL; i++) {
    char *line = *i;

    /* Skip blank lines */
    if (line[0] == '\0') continue;

    /* Split the line in 2 at the colon */
    char *colon = strchr (line, ':');
    if (colon) {
      if (colon - line == fieldlen &&
          memcmp (line, field, fieldlen) == 0)
      {
        /* The value starts after the colon */
        char *value = colon + 1;

        /* Skip any leading whitespace */
        value += strspn (value, " \t");

        /* Extract the actual information from the field. */
        char *ret = extract (value);
        if (ret == NULL) {
          /* The extraction function already sends the error. */
          return NULL;
        }

        return ret;
      }
    } else {
      /* Ignore lines with no colon. Log to stderr so it will show up in
       * LIBGUESTFS_DEBUG. */
      if (verbose) {
        fprintf (stderr, "get-gpt-type: unexpected sgdisk output ignored: %s\n",
                 line);
      }
    }
  }

  /* If we got here it means we didn't find the field */
  reply_with_error ("sgdisk output did not contain '%s'. "
                    "See LIBGUESTFS_DEBUG output for more details", field);
  return NULL;
}

static char *
extract_uuid (const char *value)
{
  /* The value contains only valid GUID characters */
  size_t value_len = strspn (value, "-0123456789ABCDEF");

  char *ret = malloc (value_len + 1);
  if (ret == NULL) {
    reply_with_perror ("malloc");
    return NULL;
  }

  memcpy (ret, value, value_len);
  ret[value_len] = '\0';
  return ret;
}

char *
do_part_get_gpt_type (const char *device, int partnum)
{
  return sgdisk_info_extract_field (device, partnum,
                                    "Partition GUID code", extract_uuid);
}

char *
do_part_get_gpt_guid (const char *device, int partnum)
{
  return sgdisk_info_extract_field (device, partnum,
                                    "Partition unique GUID", extract_uuid);
}

char *
do_part_get_name (const char *device, int partnum)
{
  CLEANUP_FREE char *parttype;

  parttype = do_part_get_parttype (device);
  if (parttype == NULL)
    return NULL;

  if (STREQ (parttype, "gpt")) {
    int parted_has_m_opt = test_parted_m_opt ();
    if (parted_has_m_opt == -1)
      return NULL;

    CLEANUP_FREE char *out = print_partition_table (device, parted_has_m_opt);
    if (!out)
      return NULL;

    if (parted_has_m_opt) {
      /* New-style parsing using the "machine-readable" format from
       * 'parted -m'.
       */
      CLEANUP_FREE_STRING_LIST char **lines = split_lines (out);

      if (!lines)
        return NULL;

      if (lines[0] == NULL || STRNEQ (lines[0], "BYT;")) {
        reply_with_error ("unknown signature, expected \"BYT;\" as first line of the output: %s",
                          lines[0] ? lines[0] : "(signature was null)");
        return NULL;
      }

      if (lines[1] == NULL) {
        reply_with_error ("parted didn't return a line describing the device");
        return NULL;
      }

      size_t row;
      int pnum;
      for (row = 2; lines[row] != NULL; ++row) {
        if (sscanf (lines[row], "%d:", &pnum) != 1) {
          reply_with_error ("could not parse row from output of parted print command: %s", lines[row]);
          return NULL;
        }
        if (pnum == partnum)
          break;
      }

      if (lines[row] == NULL) {
        reply_with_error ("partition number %d not found", partnum);
        return NULL;
      }

      char *name = get_table_field (lines[row], 5);
      if (name == NULL)
        reply_with_error ("cannot get the name field from '%s'", lines[row]);

      return name;
    }
  } else {
    reply_with_error ("part-get-name can only be used on GUID Partition Tables");
    return NULL;
  }

  reply_with_error ("cannot get the partition name from '%s' layouts", parttype);
  return NULL;
}