From: Martin Wilck <mwilck@xxxxxxxx>
The code in find_unused_loop_device() goes through circles to
get an unused device, but it takes no care not to race with a different
process opening the same loop device. Use the once-opened
loop device for setup immediately instead of closing and re-opening it.
While at it, simplify the code somewhat.
Signed-off-by: Martin Wilck <mwilck@xxxxxxxx>
---
kpartx/kpartx.c | 4 +--
kpartx/lopart.c | 72 +++++++++++++++++++------------------------------
kpartx/lopart.h | 3 +--
3 files changed, 29 insertions(+), 50 deletions(-)
diff --git a/kpartx/kpartx.c b/kpartx/kpartx.c
index 7bc6454..3c49999 100644
--- a/kpartx/kpartx.c
+++ b/kpartx/kpartx.c
@@ -359,9 +359,7 @@ main(int argc, char **argv){
exit (0);
if (!loopdev) {
- loopdev = find_unused_loop_device();
-
- if (set_loop(loopdev, rpath, 0, &ro)) {
+ if (set_loop(&loopdev, rpath, 0, &ro)) {
fprintf(stderr, "can't set up loop\n");
exit (1);
}
diff --git a/kpartx/lopart.c b/kpartx/lopart.c
index 2661940..fccb522 100644
--- a/kpartx/lopart.c
+++ b/kpartx/lopart.c
@@ -39,24 +39,6 @@
#define LOOP_CTL_GET_FREE 0x4C82
#endif
-static char *
-xstrdup (const char *s)
-{
- char *t;
-
- if (s == NULL)
- return NULL;
-
- t = strdup (s);
-
- if (t == NULL) {
- fprintf(stderr, "not enough memory");
- exit(1);
- }
-
- return t;
-}
-
#define SIZE(a) (sizeof(a)/sizeof(a[0]))
char *find_loop_by_file(const char *filename)
@@ -157,9 +139,9 @@ char *find_loop_by_file(const char *filename)
return found;
}
-char *find_unused_loop_device(void)
+static char *find_unused_loop_device(int mode, int *loop_fd)
{
- char dev[21], *next_loop_dev = NULL;
+ char dev[21];
int fd, next_loop = 0, somedev = 0, someloop = 0, loop_known = 0;
int next_loop_fd;
struct stat statbuf;
@@ -168,45 +150,47 @@ char *find_unused_loop_device(void)
next_loop_fd = open("/dev/loop-control", O_RDWR);
if (next_loop_fd < 0)
- return NULL;
+ goto nothing_found;
- if (!(fstat(next_loop_fd, &statbuf) == 0 && S_ISCHR(statbuf.st_mode))) {
- close(next_loop_fd);
- return NULL;
- }
+ if (!(fstat(next_loop_fd, &statbuf) == 0 && S_ISCHR(statbuf.st_mode)))
+ goto nothing_found;
- while (next_loop_dev == NULL) {
+ for (;;) {
next_loop = ioctl(next_loop_fd, LOOP_CTL_GET_FREE);
- if (next_loop < 0) {
- close(next_loop_fd);
- return NULL;
- }
+ if (next_loop < 0)
+ goto nothing_found;
+
sprintf(dev, "/dev/loop%d", next_loop);
- fd = open (dev, O_RDONLY);
+ fd = open (dev, mode);
if (fd >= 0) {
if (fstat (fd, &statbuf) == 0 &&
S_ISBLK(statbuf.st_mode)) {
somedev++;
if(ioctl (fd, LOOP_GET_STATUS, &loopinfo) == 0)
someloop++; /* in use */
- else if (errno == ENXIO)
- next_loop_dev = xstrdup(dev);
+ else if (errno == ENXIO) {
+ char *name = strdup(dev);
+
+ if (name == NULL)
+ close(fd);
+ else
+ *loop_fd = fd;
+ close(next_loop_fd);
+ return name;
+ }
}
close (fd);
/* continue trying as long as devices exist */
- continue;
- }
- break;
+ } else
+ break;
}
+nothing_found:
close(next_loop_fd);
- if (next_loop_dev)
- return next_loop_dev;
-
/* Nothing found. Why not? */
if ((procdev = fopen(PROC_DEVICES, "r")) != NULL) {
char line[100];
@@ -248,10 +232,10 @@ char *find_unused_loop_device(void)
return NULL;
}
-int set_loop(const char *device, const char *file, int offset, int *loopro)
+int set_loop(char **device, const char *file, int offset, int *loopro)
{
struct loop_info loopinfo;
- int fd, ffd, mode;
+ int fd = -1, ffd, mode;
mode = (*loopro ? O_RDONLY : O_RDWR);
@@ -266,11 +250,9 @@ int set_loop(const char *device, const char *file, int offset, int *loopro)
}
}
- if ((fd = open (device, mode)) < 0) {
- close(ffd);
- perror (device);
+ *device = find_unused_loop_device(mode, &fd);
+ if (!*device)
return 1;
- }
*loopro = (mode == O_RDONLY);
memset (&loopinfo, 0, sizeof (loopinfo));
diff --git a/kpartx/lopart.h b/kpartx/lopart.h
index d3bad10..c73ab23 100644
--- a/kpartx/lopart.h
+++ b/kpartx/lopart.h
@@ -1,5 +1,4 @@
extern int verbose;
-extern int set_loop (const char *, const char *, int, int *);
+extern int set_loop (char **, const char *, int, int *);
extern int del_loop (const char *);
-extern char * find_unused_loop_device (void);
extern char * find_loop_by_file (const char *);
--
2.33.1
--
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