sfdisk: add --lock and LOCK_BLOCK_DEVICE

Addresses: https://github.com/karelzak/util-linux/issues/921
Signed-off-by: Karel Zak <kzak@redhat.com>

diff --git a/disk-utils/sfdisk.8 b/disk-utils/sfdisk.8
index 5cccfa70cdf91d83e081390e8e54eb05bd20b2a4..819efee90083d7569453802bf9208253bbe0ba5d 100644 (file)
--- a/disk-utils/sfdisk.8
+++ b/disk-utils/sfdisk.8
@@ -63,17 +63,8 @@ partitions.
 uses BLKRRPART (reread partition table) ioctl to make sure that the device is
 not used by system or another tools (see also \-\-no-reread).  It's possible that
 this feature or another sfdisk activity races with \fBudevd\fR.  The recommended way
-how to avoid possible collisions is to use exclusive flock for the whole-disk
-device to serialize device access.  The exclusive lock will cause udevd to skip
-the event handling on the device.  For example:
-.RS
-.sp
-.nf
-.B "flock /dev/sdc sfdisk /dev/sdc"
-.fi
-.sp
-.RE
-Note, this semantic is not currently supported by udevd for MD and DM devices.
+how to avoid possible collisions is to use \fB\-\-lock\fR option.
+The exclusive lock will cause udevd to skip the event handling on the device. 
 .PP
 The sfdisk prompt is only a hint for users and a displayed partition number does
 not mean that the same partition table entry will be created (if -N not
@@ -221,6 +212,14 @@ Disable all consistency checking.
 Deprecated and ignored option.  Partitioning that is compatible with
 Linux (and other modern operating systems) is the default.
 .TP
+\fB\-\-lock\fR[=\fImode\fR]
+Use exclusive BSD lock for device or file it operates.  The optional argument
+\fImode\fP can be \fByes\fR, \fBno\fR (or 1 and 0) or \fBnonblock\fR.  If the \fImode\fR
+argument is omitted, it defaults to \fB"yes"\fR.  This option overwrites
+environment variable \fB$LOCK_BLOCK_DEVICE\fR.  The default is not to use any
+lock at all, but it's recommended to avoid collisions with udevd or other
+tools.
+.TP
 .BR \-n , " \-\-no\-act"
 Do everything except writing to the device.
 .TP
@@ -610,6 +609,8 @@ enables libfdisk debug output.
 enables libblkid debug output.
 .IP LIBSMARTCOLS_DEBUG=all
 enables libsmartcols debug output.
+.IP LOCK_BLOCK_DEVICE=<mode>
+use exclusive BSD lock.  The mode is "1" or "0".  See \fB\-\-lock\fR for more details.
 
 .SH NOTES
 Since version 2.26 \fBsfdisk\fR no longer provides the \fB\-R\fR or

diff --git a/disk-utils/sfdisk.c b/disk-utils/sfdisk.c
index e0c25fde76aa1986bccbdf177cc2eb473075df4b..192e9f951e0b6ccfd3853a2008c2894ca2b2983e 100644 (file)
--- a/disk-utils/sfdisk.c
+++ b/disk-utils/sfdisk.c
@@ -96,6 +96,7 @@ struct sfdisk {
        int             partno;         /* -N <partno>, default -1 */
        int             wipemode;       /* remove foreign signatures from disk */
        int             pwipemode;      /* remove foreign signatures from partitions */
+       const char      *lockmode;      /* as specified by --lock */
        const char      *label;         /* --label <label> */
        const char      *label_nested;  /* --label-nested <label> */
        const char      *backup_file;   /* -O <path> */
@@ -369,6 +370,25 @@ static void backup_partition_table(struct sfdisk *sf, const char *devname)
        free(tpl);
 }
 
+static int assign_device(struct sfdisk *sf, const char *devname, int rdonly)
+{
+       struct fdisk_context *cxt = sf->cxt;
+
+       if (fdisk_assign_device(cxt, devname, rdonly) != 0)
+               err(EXIT_FAILURE, _("cannot open %s"), devname);
+
+       if (!fdisk_is_readonly(cxt)) {
+               if (blkdev_lock(fdisk_get_devfd(cxt), devname, sf->lockmode) != 0) {
+                       fdisk_deassign_device(cxt, 1);
+                       exit(EXIT_FAILURE);
+               }
+               if (sf->backup)
+                       backup_partition_table(sf, devname);
+       }
+       return 0;
+}
+
+
 static int move_partition_data(struct sfdisk *sf, size_t partno, struct fdisk_partition *orig_pa)
 {
        struct fdisk_partition *pa = get_partition(sf->cxt, partno);
@@ -724,10 +744,7 @@ static int verify_device(struct sfdisk *sf, const char *devname)
 
        fdisk_enable_listonly(sf->cxt, 1);
 
-       if (fdisk_assign_device(sf->cxt, devname, 1)) {
-               warn(_("cannot open %s"), devname);
-               return 1;
-       }
+       assign_device(sf, devname, 1);
 
        color_scheme_enable("header", UL_COLOR_BOLD);
        fdisk_info(sf->cxt, "%s:", devname);
@@ -834,10 +851,7 @@ static int print_geom(struct sfdisk *sf, const char *devname)
 {
        fdisk_enable_listonly(sf->cxt, 1);
 
-       if (fdisk_assign_device(sf->cxt, devname, 1)) {
-               warn(_("cannot open %s"), devname);
-               return 1;
-       }
+       assign_device(sf, devname, 1);
 
        fdisk_info(sf->cxt, "%s: %ju cylinders, %ju heads, %ju sectors/track",
                        devname,
@@ -892,9 +906,7 @@ static int command_activate(struct sfdisk *sf, int argc, char **argv)
        /*  --activate <device> */
        listonly = argc == 1;
 
-       rc = fdisk_assign_device(sf->cxt, devname, listonly);
-       if (rc)
-               err(EXIT_FAILURE, _("cannot open %s"), devname);
+       assign_device(sf, devname, listonly);
 
        if (fdisk_is_label(sf->cxt, GPT)) {
                if (fdisk_gpt_is_hybrid(sf->cxt))
@@ -909,9 +921,6 @@ static int command_activate(struct sfdisk *sf, int argc, char **argv)
        } else if (!fdisk_is_label(sf->cxt, DOS))
                errx(EXIT_FAILURE, _("toggle boot flags is supported for MBR or PMBR only"));
 
-       if (!listonly && sf->backup)
-               backup_partition_table(sf, devname);
-
        nparts = fdisk_get_npartitions(sf->cxt);
        for (i = 0; i < nparts; i++) {
                char *data = NULL;
@@ -972,11 +981,7 @@ static int command_delete(struct sfdisk *sf, int argc, char **argv)
                errx(EXIT_FAILURE, _("no disk device specified"));
        devname = argv[0];
 
-       if (fdisk_assign_device(sf->cxt, devname, 0) != 0)
-               err(EXIT_FAILURE, _("cannot open %s"), devname);
-
-       if (sf->backup)
-               backup_partition_table(sf, devname);
+       assign_device(sf, devname, 0);
 
        /* delete all */
        if (argc == 1) {
@@ -1012,12 +1017,7 @@ static int command_reorder(struct sfdisk *sf, int argc, char **argv)
        if (!devname)
                errx(EXIT_FAILURE, _("no disk device specified"));
 
-       rc = fdisk_assign_device(sf->cxt, devname, 0);  /* read-write */
-       if (rc)
-               err(EXIT_FAILURE, _("cannot open %s"), devname);
-
-       if (sf->backup)
-               backup_partition_table(sf, devname);
+       assign_device(sf, devname, 0);  /* read-write */
 
        if (fdisk_reorder_partitions(sf->cxt) == 1)     /* unchanged */
                rc = fdisk_deassign_device(sf->cxt, 1);
@@ -1042,9 +1042,7 @@ static int command_dump(struct sfdisk *sf, int argc, char **argv)
        if (!devname)
                errx(EXIT_FAILURE, _("no disk device specified"));
 
-       rc = fdisk_assign_device(sf->cxt, devname, 1);  /* read-only */
-       if (rc)
-               err(EXIT_FAILURE, _("cannot open %s"), devname);
+       assign_device(sf, devname, 1);  /* read-only */
 
        if (!fdisk_has_label(sf->cxt))
                errx(EXIT_FAILURE, _("%s: does not contain a recognized partition table"), devname);
@@ -1083,6 +1081,11 @@ static void assign_device_partition(struct sfdisk *sf,
        if (rc)
                err(EXIT_FAILURE, _("cannot open %s"), devname);
 
+       if (!fdisk_is_readonly(sf->cxt)
+           && blkdev_lock(fdisk_get_devfd(sf->cxt), devname, sf->lockmode) != 0) {
+               fdisk_deassign_device(sf->cxt, 1);
+               return;
+       }
        lb = fdisk_get_label(sf->cxt, NULL);
        if (!lb)
                errx(EXIT_FAILURE, _("%s: no partition table found"), devname);
@@ -1346,8 +1349,7 @@ static int command_diskid(struct sfdisk *sf, int argc, char **argv)
        else if (argc > 2)
                errx(EXIT_FAILURE, _("unexpected arguments"));
 
-       if (fdisk_assign_device(sf->cxt, devname, !str) != 0)
-               err(EXIT_FAILURE, _("cannot open %s"), devname);
+       assign_device(sf, devname, !str);
 
        /* print */
        if (!str) {
@@ -1359,10 +1361,6 @@ static int command_diskid(struct sfdisk *sf, int argc, char **argv)
                return 0;
        }
 
-       /* change */
-       if (sf->backup)
-               backup_partition_table(sf, devname);
-
        if (fdisk_set_disklabel_id_from_string(sf->cxt, str) != 0)
                errx(EXIT_FAILURE, _("%s: failed to set disklabel ID"), devname);
 
@@ -1395,8 +1393,7 @@ static int command_relocate(struct sfdisk *sf, int argc, char **argv)
        else if (strcmp(oper, "gpt-bak-std") != 0)
                errx(EXIT_FAILURE, _("unsupported relocation operation"));
 
-       if (fdisk_assign_device(sf->cxt, devname, 0) != 0)
-               err(EXIT_FAILURE, _("cannot open %s"), devname);
+       assign_device(sf, devname, 0);
 
        fdisk_label_set_changed(lb, 1);
 
@@ -1720,9 +1717,7 @@ static int command_fdisk(struct sfdisk *sf, int argc, char **argv)
        if (!devname)
                errx(EXIT_FAILURE, _("no disk device specified"));
 
-       rc = fdisk_assign_device(sf->cxt, devname, 0);
-       if (rc)
-               err(EXIT_FAILURE, _("cannot open %s"), devname);
+       assign_device(sf, devname, 0);
 
        dp = fdisk_new_script(sf->cxt);
        if (!dp)
@@ -1798,9 +1793,6 @@ static int command_fdisk(struct sfdisk *sf, int argc, char **argv)
        if (fdisk_get_collision(sf->cxt))
                follow_wipe_mode(sf);
 
-       if (sf->backup)
-               backup_partition_table(sf, devname);
-
        if (!sf->quiet) {
                list_disk_geometry(sf->cxt);
                if (fdisk_has_label(sf->cxt)) {
@@ -2052,6 +2044,8 @@ static void __attribute__((__noreturn__)) usage(void)
              _("     --color[=<when>]      colorize output (%s, %s or %s)\n"), "auto", "always", "never");
        fprintf(out,
                "                             %s\n", USAGE_COLORS_DEFAULT);
+       fprintf(out,
+             _("     --lock[=<mode>]       use exclusive device lock (%s, %s or %s)\n"), "yes", "no", "nonblock");
        fputs(_(" -N, --partno <num>        specify partition number\n"), out);
        fputs(_(" -n, --no-act              do everything except write to device\n"), out);
        fputs(_("     --no-reread           do not check whether the device is in use\n"), out);
@@ -2110,6 +2104,7 @@ int main(int argc, char *argv[])
                OPT_DELETE,
                OPT_NOTELL,
                OPT_RELOCATE,
+               OPT_LOCK,
        };
 
        static const struct option longopts[] = {
@@ -2119,6 +2114,7 @@ int main(int argc, char *argv[])
                { "backup-file", required_argument, NULL, 'O' },
                { "bytes",   no_argument,       NULL, OPT_BYTES },
                { "color",   optional_argument, NULL, OPT_COLOR },
+               { "lock",    optional_argument, NULL, OPT_LOCK },
                { "delete",  no_argument,       NULL, OPT_DELETE },
                { "dump",    no_argument,       NULL, 'd' },
                { "help",    no_argument,       NULL, 'h' },
@@ -2324,6 +2320,14 @@ int main(int argc, char *argv[])
                case OPT_RELOCATE:
                        sf->act = ACT_RELOCATE;
                        break;
+               case OPT_LOCK:
+                       sf->lockmode = "1";
+                       if (optarg) {
+                               if (*optarg == '=')
+                                       optarg++;
+                               sf->lockmode = optarg;
+                       }
+                       break;
                default:
                        errtryhelp(EXIT_FAILURE);
                }