losetup: implement -r option. Closes 4033.

function                                             old     new   delta
packed_usage                                       28595   28633     +38
losetup_main                                         285     290      +5
singlemount                                          906     908      +2
set_loop                                             674     672      -2

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>

4 files changed, 17 insertions, 13 deletions

diff --git a/include/libbb.h b/include/libbb.h
index 21cbe1c..feae852 100644
--- a/include/libbb.h
+++ b/include/libbb.h
@@ -1164,7 +1164,7 @@ extern 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: 1: read-only loopdev was setup, 0: rw, < 0: error */
-extern int set_loop(char **devname, const char *file, unsigned long long offset) FAST_FUNC;
+extern int set_loop(char **devname, const char *file, unsigned long long offset, int ro) FAST_FUNC;
 
 /* Like bb_ask below, but asks on stdin with no timeout.  */
 char *bb_ask_stdin(const char * prompt) FAST_FUNC;
diff --git a/libbb/loop.c b/libbb/loop.c
index b798932..b3a5208 100644
--- a/libbb/loop.c
+++ b/libbb/loop.c
@@ -84,7 +84,7 @@ int FAST_FUNC del_loop(const char *device)
    search will re-use an existing loop device already bound to that
    file/offset if it finds one.
  */
-int FAST_FUNC set_loop(char **device, const char *file, unsigned long long offset)
+int FAST_FUNC set_loop(char **device, const char *file, unsigned long long offset, int ro)
 {
 	char dev[LOOP_NAMESIZE];
 	char *try;
@@ -93,11 +93,13 @@ int FAST_FUNC set_loop(char **device, const char *file, unsigned long long offse
 	int i, dfd, ffd, mode, rc = -1;
 
 	/* Open the file.  Barf if this doesn't work.  */
-	mode = O_RDWR;
+	mode = ro ? O_RDONLY : O_RDWR;
 	ffd = open(file, mode);
 	if (ffd < 0) {
-		mode = O_RDONLY;
-		ffd = open(file, mode);
+		if (mode != O_RDONLY) {
+			mode = O_RDONLY;
+			ffd = open(file, mode);
+		}
 		if (ffd < 0)
 			return -errno;
 	}
diff --git a/util-linux/losetup.c b/util-linux/losetup.c
index 9b7c49f..21108d0 100644
--- a/util-linux/losetup.c
+++ b/util-linux/losetup.c
@@ -8,11 +8,12 @@
  */
 
 //usage:#define losetup_trivial_usage
-//usage:       "[-o OFS] LOOPDEV FILE - associate loop devices\n"
+//usage:       "[-r] [-o OFS] LOOPDEV FILE - associate loop devices\n"
 //usage:       "	losetup -d LOOPDEV - disassociate\n"
 //usage:       "	losetup [-f] - show"
 //usage:#define losetup_full_usage "\n\n"
 //usage:       "	-o OFS	Start OFS bytes into FILE"
+//usage:     "\n	-r	Read-only"
 //usage:     "\n	-f	Show first free loop device"
 //usage:
 //usage:#define losetup_notes_usage
@@ -37,11 +38,12 @@ int losetup_main(int argc UNUSED_PARAM, char **argv)
 		OPT_d = (1 << 0),
 		OPT_o = (1 << 1),
 		OPT_f = (1 << 2),
+		OPT_r = (1 << 3), /* must be last */
 	};
 
-	/* max 2 args, all opts are mutually exclusive */
+	/* max 2 args, -d,-o,-f opts are mutually exclusive */
 	opt_complementary = "?2:d--of:o--df:f--do";
-	opt = getopt32(argv, "do:f", &opt_o);
+	opt = getopt32(argv, "do:fr", &opt_o);
 	argv += optind;
 
 	if (opt == OPT_o)
@@ -63,12 +65,12 @@ int losetup_main(int argc UNUSED_PARAM, char **argv)
 			bb_show_usage();
 
 		if (argv[1]) {
-			/* [-o OFS] BLOCKDEV FILE */
-			if (set_loop(&argv[0], argv[1], offset) < 0)
+			/* [-r] [-o OFS] BLOCKDEV FILE */
+			if (set_loop(&argv[0], argv[1], offset, (opt / OPT_r)) < 0)
 				bb_simple_perror_msg_and_die(argv[0]);
 			return EXIT_SUCCESS;
 		}
-		/* [-o OFS] BLOCKDEV */
+		/* [-r] [-o OFS] BLOCKDEV */
 		s = query_loop(argv[0]);
 		if (!s)
 			bb_simple_perror_msg_and_die(argv[0]);
@@ -78,7 +80,7 @@ int losetup_main(int argc UNUSED_PARAM, char **argv)
 		return EXIT_SUCCESS;
 	}
 
-	/* [-o OFS|-f] with no params */
+	/* [-r] [-o OFS|-f] with no params */
 	n = 0;
 	while (1) {
 		char *s;
diff --git a/util-linux/mount.c b/util-linux/mount.c
index 05e532c..b51ab17 100644
--- a/util-linux/mount.c
+++ b/util-linux/mount.c
@@ -1809,7 +1809,7 @@ static int singlemount(struct mntent *mp, int ignore_busy)
 		if (ENABLE_FEATURE_MOUNT_LOOP && S_ISREG(st.st_mode)) {
 			loopFile = bb_simplify_path(mp->mnt_fsname);
 			mp->mnt_fsname = NULL; // will receive malloced loop dev name
-			if (set_loop(&mp->mnt_fsname, loopFile, 0) < 0) {
+			if (set_loop(&mp->mnt_fsname, loopFile, 0, /*ro:*/ 0) < 0) {
 				if (errno == EPERM || errno == EACCES)
 					bb_error_msg(bb_msg_perm_denied_are_you_root);
 				else