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lib/blkdev: add support for --lock and LOCK_BLOCK_DEVICE 

All simple function to parse --lock <mode> and $LOCK_BLOCK_DEVICE,
and to flock the fd.

The supported <mode> is:

	"1" or "yes"	- LOCK_EX
	"0" or "no"	- do nothing
	"nonblock"	- LOCK_EX | LOCK_NB

The function tries LOCK_NB before the solo LOCK_EX and prints
inform user that it will wait, for example:

session A:
	# sfdisk --lock /dev/sdc

session B:
	# sfdisk --lock /dev/sdc
	sfdisk: /dev/sdc: device already locked, waiting to get lock ...
	^C

	# sfdisk --lock=nonblock /dev/sdc
	sfdisk: /dev/sdc: device already locked

Addresses: https://github.com/karelzak/util-linux/issues/921
Signed-off-by: Karel Zak <kzak@redhat.com>
This commit is contained in:
Karel Zak 2020-05-26 17:21:04 +02:00
parent 498f910eeb
commit 37b302046a
2 changed files with 53 additions and 0 deletions
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1
include/blkdev.h
View File

@ -146,5 +146,6 @@ int blkdev_get_geometry(int fd, unsigned int *h, unsigned int *s);
/* convert scsi type code to name */
const char *blkdev_scsi_type_to_name(int type);
int blkdev_lock(int fd, const char *devname, const char *lockmode);
#endif /* BLKDEV_H */

52
lib/blkdev.c
View File

@ -6,6 +6,7 @@
*/
#include <sys/types.h>
#include <sys/stat.h>
#include <sys/file.h>
#include <sys/ioctl.h>
#include <unistd.h>
#include <stdint.h>
@ -361,6 +362,57 @@ const char *blkdev_scsi_type_to_name(int type)
return NULL;
}
/* return 0 on success */
int blkdev_lock(int fd, const char *devname, const char *lockmode)
{
int oper, rc, msg = 0;
if (!lockmode)
lockmode = getenv("LOCK_BLOCK_DEVICE");
if (!lockmode)
return 0;
if (strcasecmp(lockmode, "yes") == 0 ||
strcmp(lockmode, "1") == 0)
oper = LOCK_EX;
else if (strcasecmp(lockmode, "nonblock") == 0)
oper = LOCK_EX | LOCK_NB;
else if (strcasecmp(lockmode, "no") == 0 ||
strcmp(lockmode, "0") == 0)
return 0;
else {
warnx(_("unsupported lock mode: %s"), lockmode);
return -EINVAL;
}
if (!(oper & LOCK_NB)) {
/* Try non-block first to provide message */
rc = flock(fd, oper | LOCK_NB);
if (rc == 0)
return 0;
if (rc != 0 && errno == EWOULDBLOCK) {
fprintf(stderr, _("%s: %s: device already locked, waiting to get lock ... "),
program_invocation_short_name, devname);
msg = 1;
}
}
rc = flock(fd, oper);
if (rc != 0) {
switch (errno) {
case EWOULDBLOCK: /* LOCK_NB */
warnx(_("%s: device already locked"), devname);
break;
default:
warn(_("%s: failed to get lock"), devname);
}
} else if (msg)
fprintf(stderr, _("OK\n"));
return rc;
}
#ifdef TEST_PROGRAM_BLKDEV
#include <stdio.h>
#include <stdlib.h>