blkdiscard: use O_EXCL, add --force

Let's make it more robust and safe. O_EXCL is an elegant way how to avoid
unwanted discard on mounted device.

Addresses: https://github.com/karelzak/util-linux/issues/915
Signed-off-by: Karel Zak <kzak@redhat.com>

diff --git a/sys-utils/blkdiscard.8 b/sys-utils/blkdiscard.8
index 1f3a32be9f039922b5125e039bcbb94f605f9a13..98c6f36a98a74215bbb3b1f8fea06b61a008bf2e 100644 (file)
--- a/sys-utils/blkdiscard.8
+++ b/sys-utils/blkdiscard.8
@@ -36,6 +36,11 @@ MiB (=1024*1024), and so on for GiB, TiB, PiB, EiB, ZiB and YiB (the "iB" is
 optional, e.g., "K" has the same meaning as "KiB") or the suffixes
 KB (=1000), MB (=1000*1000), and so on for GB, TB, PB, EB, ZB and YB.
 .TP
+.BR \-f , " \-\-force"
+Disable all checking.  Since v2.36 the block device is open in exclusive mode (O_EXCL)
+by default to avoid collision with mounted filesystem or another kernel subsystem.
+The force option disables the exclusive access mode.
+.TP
 .BR \-o , " \-\-offset \fIoffset"
 Byte offset into the device from which to start discarding.  The provided value
 will be aligned to the device sector size.  The default value is zero.

diff --git a/sys-utils/blkdiscard.c b/sys-utils/blkdiscard.c
index f9ba5e468e38be2d4f69f7d88a2a322fdd6ef8a5..589974f9c4bcb580943768adc1378f22c3cc74fd 100644 (file)
--- a/sys-utils/blkdiscard.c
+++ b/sys-utils/blkdiscard.c
@@ -88,6 +88,7 @@ static void __attribute__((__noreturn__)) usage(void)
        fputs(_("Discard the content of sectors on a device.\n"), out);
 
        fputs(USAGE_OPTIONS, out);
+       fputs(_(" -f, --force         disable all checking\n"), out);
        fputs(_(" -o, --offset <num>  offset in bytes to discard from\n"), out);
        fputs(_(" -l, --length <num>  length of bytes to discard from the offset\n"), out);
        fputs(_(" -p, --step <num>    size of the discard iterations within the offset\n"), out);
@@ -106,7 +107,7 @@ static void __attribute__((__noreturn__)) usage(void)
 int main(int argc, char **argv)
 {
        char *path;
-       int c, fd, verbose = 0, secsize;
+       int c, fd, verbose = 0, secsize, force = 0;
        uint64_t end, blksize, step, range[2], stats[2];
        struct stat sb;
        struct timeval now, last;
@@ -116,6 +117,7 @@ int main(int argc, char **argv)
            { "help",      no_argument,       NULL, 'h' },
            { "version",   no_argument,       NULL, 'V' },
            { "offset",    required_argument, NULL, 'o' },
+           { "force",     no_argument,       NULL, 'f' },
            { "length",    required_argument, NULL, 'l' },
            { "step",      required_argument, NULL, 'p' },
            { "secure",    no_argument,       NULL, 's' },
@@ -133,8 +135,11 @@ int main(int argc, char **argv)
        range[1] = ULLONG_MAX;
        step = 0;
 
-       while ((c = getopt_long(argc, argv, "hVsvo:l:p:z", longopts, NULL)) != -1) {
+       while ((c = getopt_long(argc, argv, "hfVsvo:l:p:z", longopts, NULL)) != -1) {
                switch(c) {
+               case 'f':
+                       force = 1;
+                       break;
                case 'l':
                        range[1] = strtosize_or_err(optarg,
                                        _("failed to parse length"));
@@ -176,7 +181,7 @@ int main(int argc, char **argv)
                errtryhelp(EXIT_FAILURE);
        }
 
-       fd = open(path, O_WRONLY);
+       fd = open(path, O_WRONLY | (force ? 0 : O_EXCL));
        if (fd < 0)
                err(EXIT_FAILURE, _("cannot open %s"), path);