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mount,losetup: use /dev/loop-control is it exists

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function                                             old     new   delta
get_free_loop                                          -      58     +58
set_loop                                             597     649     +52
losetup_main                                         482     476      -6
------------------------------------------------------------------------------
(add/remove: 1/0 grow/shrink: 1/1 up/down: 110/-6)            Total: 104 bytes

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
This commit is contained in:
Denys Vlasenko 2019-06-09 23:20:49 +02:00
parent 7b6d4f50c9
commit 3b69ba799f
3 changed files with 47 additions and 10 deletions
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7
include/libbb.h
View File

@ -1461,14 +1461,15 @@ extern void bb_warn_ignoring_args(char *arg) FAST_FUNC;
extern int get_linux_version_code(void) FAST_FUNC;
extern char *query_loop(const char *device) FAST_FUNC;
extern int del_loop(const char *device) FAST_FUNC;
char *query_loop(const char *device) FAST_FUNC;
int get_free_loop(void) FAST_FUNC;
int del_loop(const char *device) FAST_FUNC;
/*
* If *devname is not NULL, use that name, otherwise try to find free one,
* malloc and return it in *devname.
* return value is the opened fd to the loop device, or < on error
*/
extern int set_loop(char **devname, const char *file, unsigned long long offset, unsigned flags) FAST_FUNC;
int set_loop(char **devname, const char *file, unsigned long long offset, unsigned flags) FAST_FUNC;
/* These constants match linux/loop.h (without BB_ prefix): */
#define BB_LO_FLAGS_READ_ONLY 1
#define BB_LO_FLAGS_AUTOCLEAR 4

42
libbb/loop.c
View File

@ -78,6 +78,24 @@ int FAST_FUNC del_loop(const char *device)
return rc;
}
/* Obtain an unused loop device number */
int FAST_FUNC get_free_loop(void)
{
int fd;
int loopdevno;
fd = open("/dev/loop-control", O_RDWR | O_CLOEXEC);
if (fd == -1)
return fd - 1; /* -2: "no /dev/loop-control" */
#ifndef LOOP_CTL_GET_FREE
# define LOOP_CTL_GET_FREE 0x4C82
#endif
loopdevno = ioctl(fd, LOOP_CTL_GET_FREE);
close(fd);
return loopdevno; /* can be -1 if error */
}
/* Returns opened fd to the loop device, <0 on error.
* *device is loop device to use, or if *device==NULL finds a loop device to
* mount it on and sets *device to a strdup of that loop device name. This
@ -106,12 +124,24 @@ int FAST_FUNC set_loop(char **device, const char *file, unsigned long long offse
return -errno;
}
//TODO: use LOOP_CTL_GET_FREE instead of trying every loopN in sequence? a-la:
// fd = open("/dev/loop-control", O_RDWR);
// loopN = ioctl(fd, LOOP_CTL_GET_FREE);
//
try = *device;
if (!try) {
i = get_free_loop();
if (i == -2) { /* no /dev/loop-control */
i = 0;
try = dev;
goto old_style;
}
if (i == -1) {
close(ffd);
return -1; /* no free loop devices */
}
try = *device = xasprintf(LOOP_FORMAT, i);
goto try_to_open;
}
old_style:
/* Find a loop device. */
try = *device ? *device : dev;
/* 1048575 (0xfffff) is a max possible minor number in Linux circa 2010 */
for (i = 0; rc && i < 1048576; i++) {
sprintf(dev, LOOP_FORMAT, i);
@ -170,7 +200,7 @@ int FAST_FUNC set_loop(char **device, const char *file, unsigned long long offse
rc = ioctl(dfd, BB_LOOP_SET_STATUS, &loopinfo);
}
if (rc != 0) {
ioctl(dfd, LOOP_CLR_FD, 0);
ioctl(dfd, LOOP_CLR_FD, 0); // actually, 0 param is unnecessary
}
}
} else {

8
util-linux/losetup.c
View File

@ -114,8 +114,14 @@ int losetup_main(int argc UNUSED_PARAM, char **argv)
/* contains -f */
if (opt & OPT_f) {
char *s;
int n = 0;
int n;
n = get_free_loop();
if (n == -1)
bb_error_msg_and_die("no free loop devices");
if (n < 0) /* n == -2: no /dev/loop-control, use legacy method */
n = 0;
/* or: n >= 0: the number of next free loopdev, just verify it */
do {
if (n > MAX_LOOP_NUM)
bb_error_msg_and_die("no free loop devices");