Hello,
I write to you because I believe that the BLKPG ioctl misbehaves when an
existing extended MBR partition is changed and a logical partition added
in it.
Should I report like this or should I sign up for bugzilla.kernel.org?
The /sys/block/sdx/sdxY/size entry is set to 0 and even opening the
extended partition fails.
This leads to e.g. udevd failing to have access.
https://github.com/storaged-project/udisks/issues/425
To fix this situation from userspace, a BLKRRPART ioctl is needed.
To reproduce it, I attached a small program, which you can run on this
prepared image or on any drive with a single extended partition on it.
$ wget http://kailueke.spline.de/test.img
$ udisksctl loop-setup -f test.img
$ sudo ./sim loop0
new size in /sys/block/loop0/loop0p1/size: 0
issuing BLKRRPART
new size in /sys/block/loop0/loop0p1/size: 2
Do you think that this should be fixed in the kernel?
Regards,
Kai Lüke
#include <errno.h>
#include <fcntl.h>
#include <linux/blkpg.h>
#include <linux/fs.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/ioctl.h>
#include <sys/stat.h>
#include <sys/types.h>
#include <unistd.h>
int resizepart(char *path, int start, int fd) {
struct blkpg_partition part;
struct blkpg_ioctl_arg ioctl_arg;
memset(&part, 0, sizeof(part));
part.start = start;
part.length = 1;
part.pno = 1;
strncpy(part.devname, path, BLKPG_DEVNAMELTH);
ioctl_arg.op = BLKPG_RESIZE_PARTITION;
ioctl_arg.flags = 0;
ioctl_arg.datalen = sizeof(struct blkpg_partition);
ioctl_arg.data = (void *)∂
if (ioctl(fd, BLKPG, &ioctl_arg) == -1) {
perror(strerror(errno));
exit(errno);
}
}
int addpart(char *path, int start, int fd) {
struct blkpg_partition part;
struct blkpg_ioctl_arg ioctl_arg;
memset(&part, 0, sizeof(part));
part.start = start + 2097152;
part.length = 10485760; /* 10 MB */
part.pno = 5;
strncpy(part.devname, path, BLKPG_DEVNAMELTH);
ioctl_arg.op = BLKPG_ADD_PARTITION;
ioctl_arg.flags = 0;
ioctl_arg.datalen = sizeof(struct blkpg_partition);
ioctl_arg.data = (void *)∂
if (ioctl(fd, BLKPG, &ioctl_arg) == -1) {
perror(strerror(errno));
exit(errno);
}
}
int main(int argc, char **argv) {
char *disk;
char *existing_extended_part;
char *new_logical_part;
int fd;
int read_fd;
char path[100];
char buf[100];
int start;
const char *loopback = "";
if (argc != 2) {
printf("Usage: %s sdb \nAnnounces a logical sdb5 partition to the kernel "
"on MBR drive /dev/sdb, which must only have a single extended "
"partition (sdb1) and no logical partitons present yet.\nThis is "
"done with BLKPG calls to issue a resize call for sdb1 and an add "
"call for sdb5.\nThe observed problem is that the kernel then has a "
"zero size for the extended partition (thus, nothing can access it "
"anymore). Only a BLKRRPART can fix it again, as will be done here "
"when a zero size is detected.\n\nEven when the BLKRRPART is "
"removed here,"
"after this program ends, udev will anyway trigger a BLKRRPART,"
"therefore, you may have to pause udevd if it is"
"interfering with a command you want to run afterwards:\n"
"sudo kill -s STOP `pgrep udevd`\nThen, after running all you "
"commands, "
"you can continue udevd again:\nsudo kill -s CONT `pgrep udevd`",
argv[0]);
return -1;
}
disk = argv[1];
if (strncmp(disk, "loop", 4) == 0)
loopback = "p";
memset(path, 0, sizeof(path));
snprintf(path, sizeof(path), "/sys/block/%s/%s%s1/start", disk, disk,
loopback);
read_fd = open(path, O_RDONLY);
if (read_fd == -1) {
perror(strerror(errno));
exit(errno);
}
memset(buf, 0, sizeof(buf));
if (read(read_fd, buf, sizeof(buf)) == -1)
return -1;
close(read_fd);
start = atoi(buf) * 512;
memset(path, 0, sizeof(path));
snprintf(path, sizeof(path), "/dev/%s", disk);
fd = open(path, O_RDWR);
if (fd == -1) {
perror(strerror(errno));
exit(errno);
}
/* order can be reversed to add/resize and the result is still the same:
* /sys/block/sdb/sdb1/size containing a 0 instead of 1 or 2 */
memset(path, 0, sizeof(path));
snprintf(path, sizeof(path), "/dev/%s%s1", disk, loopback);
resizepart(path, start, fd);
memset(path, 0, sizeof(path));
snprintf(path, sizeof(path), "/dev/%s%s5", disk, loopback);
addpart(path, start, fd);
/* even adding this again as last step does not help */
memset(path, 0, sizeof(path));
snprintf(path, sizeof(path), "/dev/%s%s1", disk, loopback);
resizepart(path, start, fd);
/* fetch value now for convenience and also because no interfering BLKRRPART
* was done yet by other programs */
memset(path, 0, sizeof(path));
snprintf(path, sizeof(path), "/sys/block/%s/%s%s1/size", disk, disk,
loopback);
while (1) {
memset(buf, 0, sizeof(buf));
read_fd = open(path, O_RDONLY);
if (read_fd == -1 || read(read_fd, buf, sizeof(buf)) == -1) {
printf("could not fetch %s\n", path);
if (read_fd != -1)
close(read_fd);
perror(strerror(errno));
exit(errno);
}
close(read_fd);
printf("new size in %s: %s\n", path, buf);
if (atoi(buf) != 0) {
break;
}
ioctl(fd, BLKRRPART, 0);
printf("issuing BLKRRPART\n");
}
close(fd);
return 0;
}
--
dm-devel mailing list
dm-devel@xxxxxxxxxx
https://www.redhat.com/mailman/listinfo/dm-devel
