Skip to content

Commit

Permalink
Work around bug in LOOP_CTL_GET_FREE
Browse files Browse the repository at this point in the history 
LOOP_CTL_GET_FREE will happily return a loop device that is currently
being configured, even though opening such a device in exclusive mode
returns -EBUSY.  Create a new loop device instead when this happens.

Also unconditionally destroy the loop device when no longer used.
  • Loading branch information
@DemiMarie
DemiMarie committed Mar 11, 2023
1 parent 3131d57 commit 98f06b4
Showing 1 changed file with 76 additions and 58 deletions.
134 changes: 76 additions & 58 deletions not-script/not-script.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -20,6 +20,7 @@
#include <linux/major.h>
#include <linux/loop.h>
#include <linux/fs.h>
#include <linux/dm-ioctl.h>

#include <xen/xen.h>
#include <xen/io/xenbus.h>
Expand Down Expand Up @@ -66,25 +67,38 @@ static int setup_loop(struct loop_context *ctx,
},
};

for (;;) {
int status = ioctl(ctx->fd, LOOP_CTL_GET_FREE);
for (;; retry_count++) {
int status = ioctl(ctx->fd, retry_count ? LOOP_CTL_ADD : LOOP_CTL_GET_FREE, -1);
if (status < 0)
err(1, "ioctl(%d, LOOP_CTL_GET_FREE)", ctx->fd);
dev_file = open_loop_dev(status, writable);
if (dev_file > 0) {
switch (ioctl(dev_file, LOOP_CONFIGURE, &config)) {
case 0:
return dev_file;
case -1:
retry_count++;
if ((errno != EBUSY && errno != ENXIO) || (retry_count > retry_limit))
err(1, "ioctl(%d, LOOP_CONFIGURE, %p)", dev_file, &config);
if (close(dev_file))
abort(); /* cannot happen on Linux */
break;
default:
abort();
err(1, "ioctl(%d, LOOP_CTL_%s)", ctx->fd, retry_count ? "ADD" : "GET_FREE");
char buf[sizeof("/dev/loop") + 10];
if ((unsigned)snprintf(buf, sizeof buf, "/dev/loop%u", (unsigned)status) >= sizeof buf)
abort();
int flags = (writable ? O_RDWR : O_RDONLY) |
O_EXCL | O_CLOEXEC | O_NOCTTY | O_NOFOLLOW;
dev_file = open(buf, flags);
if (dev_file < 0) {
assert(dev_file == -1);
if ((errno != EAGAIN && errno != EBUSY && errno != ENXIO && errno != ENOENT) ||
(retry_count >= retry_limit))
{
err(1, "open(\"%s\", %#x): retry count %d, retry limit %d",
buf, flags, retry_count, retry_limit);
}
continue;
}
switch (ioctl(dev_file, LOOP_CONFIGURE, &config)) {
case 0:
return dev_file;
case -1:
if ((errno != EBUSY && errno != ENXIO) || (retry_count >= retry_limit))
err(1, "ioctl(%d, LOOP_CONFIGURE, %p): retry count %d, retry limit %d",
dev_file, &config, retry_count, retry_limit);
if (close(dev_file))
abort(); /* cannot happen on Linux */
break;
default:
abort();
}
}
}
Expand All @@ -109,7 +123,7 @@ process_blk_dev(int fd, const char *path, bool writable, dev_t *dev,

const char *const devname = path + DEV_MAPPER_SIZE;
size_t const devname_len = strlen(devname);
if (strcmp(devname, "control") == 0 ||
if (strcmp(devname, DM_CONTROL_NODE) == 0 ||
strcmp(devname, ".") == 0 ||
strcmp(devname, "..") == 0 ||
memchr(devname, '/', devname_len) != NULL)
Expand Down Expand Up @@ -206,18 +220,24 @@ static void redirect_stderr(void)
err(1, "close(%d)", redirect_fd);
}

static bool strict_strtoul_hex(char *p, char **endp, char expected, unsigned long *res)
static bool strict_strtoul_hex(char *p, char **endp, char expected, uint64_t *res, uint64_t max)
{
if (*p == '0') {
switch (*p) {
case '0':
*res = 0;
*endp = p + 1;
} else if ((*p < '1' || *p > '9') && (*p < 'a' && *p > 'f')) {
return false;
} else {
break;
case '1'...'9':
case 'a'...'f':
case 'A'...'F':
errno = 0;
*res = strtoul(p, endp, 16);
if (*res > UINT32_MAX || errno)
unsigned long long out = strtoull(p, endp, 16);
if (out > max || errno)
return false;
*res = out;
break;
default:
return false;
}

return **endp == expected;
Expand Down Expand Up @@ -246,13 +266,13 @@ static bool get_opened(struct xs_handle *const h, char *const extra_path,
}

static void remove_device(struct xs_handle *const h, char *xenstore_path_buffer,
char *extra_path)
char *extra_path, bool autoclear)
{
char *physdev, *end_path, *diskseq_str;
unsigned int path_len, diskseq_len;
int loop_control_fd, loop_fd;
uint64_t actual_diskseq;
unsigned long _major, _minor;
uint64_t actual_diskseq, expected_diskseq;
uint64_t _major, _minor;

/*
* Order matters here: the kernel only cares about "physical-device" for
Expand All @@ -267,39 +287,37 @@ static void remove_device(struct xs_handle *const h, char *xenstore_path_buffer,
if (!xs_rm(h, 0, xenstore_path_buffer))
err(1, "xs_rm(\"%s\")", xenstore_path_buffer);

strcpy(extra_path, "diskseq");
diskseq_str = xs_read(h, 0, xenstore_path_buffer, &diskseq_len);
if (diskseq_str == NULL) {
err(1, "Cannot obtain diskseq from XenStore path %s", xenstore_path_buffer);
}
if (autoclear) {
if (!strict_strtoul_hex(physdev, &end_path, '@', &expected_diskseq, UINT64_MAX))
goto bad_physdev;
end_path++;
} else {
strcpy(extra_path, "diskseq");
diskseq_str = xs_read(h, 0, xenstore_path_buffer, &diskseq_len);
if (diskseq_str == NULL) {
err(1, "Cannot obtain diskseq from XenStore path %s", xenstore_path_buffer);
}

if (!xs_rm(h, 0, xenstore_path_buffer))
err(1, "xs_rm(\"%s\")", xenstore_path_buffer);
if (!xs_rm(h, 0, xenstore_path_buffer))
err(1, "xs_rm(\"%s\")", xenstore_path_buffer);

if (!strict_strtoul_hex(diskseq_str, &end_path, '\0', &expected_diskseq, UINT64_MAX))
errx(1, "Bad diskseq %s", diskseq_str);
end_path = physdev;
free(diskseq_str);
}

errno = 0;

if ((!strict_strtoul_hex(physdev, &end_path, ':', &_major)) ||
(!strict_strtoul_hex(end_path + 1, &end_path, '\0', &_minor)) ||
if ((!strict_strtoul_hex(end_path, &end_path, ':', &_major, UINT32_MAX)) ||
(!strict_strtoul_hex(end_path + 1, &end_path, '\0', &_minor, UINT32_MAX)) ||
(end_path != physdev + path_len)) {
goto bad_physdev;
}

if (_major != LOOP_MAJOR)
return; /* Not a loop device */

if (diskseq_len != 16)
goto bad_diskseq;

for (unsigned i = 0; i < diskseq_len; ++i) {
if ((diskseq_str[i] < '0' || diskseq_str[i] > '9') &&
(diskseq_str[i] < 'a' || diskseq_str[i] > 'f')) {
goto bad_diskseq;
}
}

unsigned long long const diskseq = strtoull(diskseq_str, &end_path, 16);
if (errno || end_path != diskseq_str + diskseq_len)
abort(); /* cannot happen due to above check */
if ((loop_control_fd = open_file("/dev/loop-control")) < 0)
err(1, "open(/dev/loop-control)");

Expand All @@ -317,10 +335,10 @@ static void remove_device(struct xs_handle *const h, char *xenstore_path_buffer,
if (ioctl(loop_fd, BLKGETDISKSEQ, &actual_diskseq))
err(1, "ioctl(%d, BLKGETDISKSEQ, %p)", loop_fd, &actual_diskseq);

if (diskseq != actual_diskseq)
if (expected_diskseq != actual_diskseq)
errx(1, "Loop device diskseq mismatch!");

if (ioctl(loop_fd, LOOP_CLR_FD))
if (!autoclear && ioctl(loop_fd, LOOP_CLR_FD))
err(1, "ioctl(\"/dev/loop%lu\", LOOP_CLR_FD)", _minor);

int res = ioctl(loop_control_fd, LOOP_CTL_REMOVE, (long)_minor);
Expand All @@ -336,8 +354,6 @@ static void remove_device(struct xs_handle *const h, char *xenstore_path_buffer,
return;
bad_physdev:
errx(1, "Bad physical device value %s", physdev);
bad_diskseq:
errx(1, "Bad diskseq %s", diskseq_str);
}


Expand Down Expand Up @@ -416,8 +432,7 @@ int main(int argc, char **argv)
action == REMOVE ? '1' : '0');

if (action == REMOVE) {
if (!autoclear)
remove_device(h, xenstore_path_buffer, extra_path);
remove_device(h, xenstore_path_buffer, extra_path, autoclear);
return 0;
}

Expand Down Expand Up @@ -500,10 +515,13 @@ int main(int argc, char **argv)

if (!autoclear) {
char hex_diskseq[17];
if (snprintf(hex_diskseq, sizeof(hex_diskseq), "%016llx", (unsigned long long)diskseq) != 16)
int diskseq_len =
snprintf(hex_diskseq, sizeof(hex_diskseq), "%llx",
(unsigned long long)diskseq);
if (diskseq_len < 1 || diskseq_len > 16)
err(1, "snprintf");
strcpy(extra_path, "diskseq");
if (!xs_write(h, t, xenstore_path_buffer, hex_diskseq, 16))
if (!xs_write(h, t, xenstore_path_buffer, hex_diskseq, diskseq_len))
err(1, "xs_write(\"%s\", \"%s\")", xenstore_path_buffer, hex_diskseq);
}

Expand Down

0 comments on commit 98f06b4

Please sign in to comment.