Adding -f option to qemu-nbd to support finding a free nbd device and connect
disk image to that device. Usage of this option is similar to "losetup -f".
#qemu-nbd -f
show the first free nbd device found at the very moment.
#qemu-nbd -f disk.img
find a free nbd device and connect disk.img to that device.
Adding lock to the nbd device before connecting disk image to that device to
handling race conditions.
Signed-off-by: Chunyan Liu <cy...@suse.com>
---
qemu-nbd.c | 90 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++-
1 files changed, 89 insertions(+), 1 deletions(-)
diff --git a/qemu-nbd.c b/qemu-nbd.c
index 291cba2..64892a8 100644
--- a/qemu-nbd.c
+++ b/qemu-nbd.c
@@ -32,6 +32,7 @@
#include <signal.h>
#include <libgen.h>
#include <pthread.h>
+#include <fcntl.h>
#define SOCKET_PATH "/var/lock/qemu-nbd-%s"
@@ -244,6 +245,60 @@ out:
return (void *) EXIT_FAILURE;
}
+static int is_nbd_used(int minor)
+{
+ FILE *proc;
+ int NBDMAJOR = 43;
+ char buf[BUFSIZ];
+ int find = 0;
+
+ proc = fopen("/proc/partitions", "r");
+ if (proc != NULL) {
+ while (fgets(buf, sizeof(buf), proc)) {
+ int m, n;
+ unsigned long long sz;
+ char name[16];
+ char *pname = name;
+ char *end;
+
+ if (sscanf(buf, " %d %d %llu %128[^\n ]",
+ &m, &n, &sz, name) != 4)
+ continue;
+ if (m != NBDMAJOR)
+ continue;
+ if (strncmp(name, "nbd", 3))
+ continue;
+ pname += 3;
+ n = strtol(pname, &end, 10);
+ if (end && end != pname && *end == '\0' && n == minor) {
+ find = 1;
+ break;
+ }
+ }
+ fclose(proc);
+ }
+
+ return find;
+}
+
+static char *find_free_nbd_device(void)
+{
+ int i;
+ int nbds_max = 16;
+ char name[16];
+ char *devname = NULL;
+
+ for (i = 0; i < nbds_max; i++) {
+ if (!is_nbd_used(i)) {
+ snprintf(name, sizeof(name), "/dev/nbd%d", i);
+ devname = strdup(name);
+ break;
+ }
+ }
+
+ return devname;
+}
+
int main(int argc, char **argv)
{
BlockDriverState *bs;
@@ -256,7 +311,7 @@ int main(int argc, char **argv)
struct sockaddr_in addr;
socklen_t addr_len = sizeof(addr);
off_t fd_size;
- const char *sopt = "hVb:o:p:rsnP:c:dvk:e:t";
+ const char *sopt = "hVb:o:p:rsnP:c:dvk:e:tf";
struct option lopt[] = {
{ "help", 0, NULL, 'h' },
{ "version", 0, NULL, 'V' },
@@ -273,6 +328,7 @@ int main(int argc, char **argv)
{ "shared", 1, NULL, 'e' },
{ "persistent", 0, NULL, 't' },
{ "verbose", 0, NULL, 'v' },
+ { "find", 0, NULL, 'f' },
{ NULL, 0, NULL, 0 }
};
int ch;
@@ -292,6 +348,9 @@ int main(int argc, char **argv)
int max_fd;
int persistent = 0;
pthread_t client_thread;
+ char *devname = NULL;
+ int find = 0;
+ struct flock lock;
/* The client thread uses SIGTERM to interrupt the server. A signal
* handler ensures that "qemu-nbd -v -c" exits with a nice status code.
@@ -374,6 +433,18 @@ int main(int argc, char **argv)
case 'v':
verbose = 1;
break;
+ case 'f':
+ find = 1;
+ devname = find_free_nbd_device();
+ if (devname == NULL)
+ exit(1);
+ if (argc == optind) {
+ printf("%s\n", devname);
+ free(devname);
+ exit(0);
+ }
+ device = devname;
+ break;
case 'V':
version(argv[0]);
exit(0);
@@ -464,11 +535,28 @@ int main(int argc, char **argv)
/* Open before spawning new threads. In the future, we may
* drop privileges after opening.
*/
+retry:
fd = open(device, O_RDWR);
if (fd == -1) {
err(EXIT_FAILURE, "Failed to open %s", device);
}
+ memset(&lock, 0, sizeof(lock));
+ lock.l_type = F_WRLCK;
+ lock.l_whence = SEEK_SET;
+ if (fcntl(fd, F_SETLK, &lock) != 0) {
+ if (find) {
+ close(fd);
+ free(device);
+ device = find_free_nbd_device();
+ if (!device)
+ err(EXIT_FAILURE, "Could not find free nbd device");
+ goto retry;
+ } else {
+ err(EXIT_FAILURE, "Could not lock %s", device);
+ }
+ }
+
if (sockpath == NULL) {
sockpath = g_malloc(128);
snprintf(sockpath, 128, SOCKET_PATH, basename(device));
--
1.7.3.4
