[PATCH v2 2/9] loop:refactor: extract subfunction get_next_free_loop()

[Xiaoming Ni]

Step 2 of micro-refactoring the set_loop function ()
	Extract subfunction get_next_free_loop() from set_loop()

Also fix miss free(try) when stat(try) and mknod fail

function                                             old     new   delta
set_loop                                             758     734     -24
------------------------------------------------------------------------------
(add/remove: 0/0 grow/shrink: 0/1 up/down: 0/-24)             Total: -24 bytes

Fixes: 3448914e8cc5 ("mount,losetup: use /dev/loop-control is it exists")
Signed-off-by: Xiaoming Ni <nixiaoming at huawei.com>
---
 libbb/loop.c | 55 ++++++++++++++++++++++++----------------------------
 1 file changed, 25 insertions(+), 30 deletions(-)

diff --git a/libbb/loop.c b/libbb/loop.c
index c517ceb13..71fd8c1bc 100644
--- a/libbb/loop.c
+++ b/libbb/loop.c
@@ -96,6 +96,20 @@ int FAST_FUNC get_free_loop(void)
 	return loopdevno; /* can be -1 if error */
 }
 
+static int get_next_free_loop(char *dev, int id)
+{
+	int i = get_free_loop();
+	if (i >= 0) {
+		sprintf(dev, LOOP_FORMAT, i);
+		return 1; /* use /dev/loop-control */
+	} else if (i == -2) {
+		sprintf(dev, LOOP_FORMAT, id);
+		return 2;
+	} else {
+		return -1; /* no free loop devices */
+	}
+}
+
 static int open_file(const char *file, unsigned flags, int *mode)
 {
 	int ffd;
@@ -132,30 +146,26 @@ int FAST_FUNC set_loop(char **device, const char *file, unsigned long long offse
 
 	try = *device;
 	if (!try) {
- get_free_loopN:
-		i = get_free_loop();
-		if (i == -1) {
-			close(ffd);
-			return -1; /* no free loop devices */
-		}
-		if (i >= 0) {
-			try = xasprintf(LOOP_FORMAT, i);
-			goto open_lfd;
-		}
-		/* i == -2: no /dev/loop-control. Do an old-style search for a free device */
 		try = dev;
 	}
 
 	/* Find a loop device */
 	/* 0xfffff is a max possible minor number in Linux circa 2010 */
 	for (i = 0; i <= 0xfffff; i++) {
-		sprintf(dev, LOOP_FORMAT, i);
+		if (!*device) {
+			rc = get_next_free_loop(dev, i);
+			if (rc == -1) {
+				break; /* no free loop devices */
+			} else if (rc == 1) {
+				goto open_lfd;
+			}
+		}
 
 		IF_FEATURE_MOUNT_LOOP_CREATE(errno = 0;)
 		if (stat(try, &statbuf) != 0 || !S_ISBLK(statbuf.st_mode)) {
 			if (ENABLE_FEATURE_MOUNT_LOOP_CREATE
 			 && errno == ENOENT
-			 && try == dev
+			 && (!*device)
 			) {
 				/* Node doesn't exist, try to create it */
 				if (mknod(dev, S_IFBLK|0644, makedev(7, i)) == 0)
@@ -188,13 +198,10 @@ int FAST_FUNC set_loop(char **device, const char *file, unsigned long long offse
 			/* Associate free loop device with file */
 			if (ioctl(lfd, LOOP_SET_FD, ffd)) {
 				/* Ouch. Are we racing with other mount? */
-				if (!*device   /* yes */
-				 && try != dev /* tried a _kernel-offered_ loopN? */
-				) {
-					free(try);
+				if (!*device) {
 					close(lfd);
 //TODO: add "if (--failcount != 0) ..."?
-					goto get_free_loopN;
+					continue;
 				}
 				goto close_and_try_next_loopN;
 			}
@@ -218,8 +225,6 @@ int FAST_FUNC set_loop(char **device, const char *file, unsigned long long offse
 			}
 			if (rc == 0) {
 				/* SUCCESS! */
-				if (try != dev) /* tried a kernel-offered free loopN? */
-					*device = try; /* malloced */
 				if (!*device)   /* was looping in search of free "/dev/loopN"? */
 					*device = xstrdup(dev);
 				rc = lfd; /* return this */
@@ -227,16 +232,6 @@ int FAST_FUNC set_loop(char **device, const char *file, unsigned long long offse
 			}
 			/* failure, undo LOOP_SET_FD */
 			ioctl(lfd, LOOP_CLR_FD, 0); // actually, 0 param is unnecessary
-		} else {
-			/* device is not free (rc == 0), or error other than ENXIO */
-			if (rc == 0	/* device is not free? */
-			 && !*device	/* racing with other mount? */
-			 && try != dev	/* tried a _kernel-offered_ loopN? */
-			) {
-				free(try);
-				close(lfd);
-				goto get_free_loopN;
-			}
 		}
  close_and_try_next_loopN:
 		close(lfd);
-- 
2.27.0