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 21cbe1cac..feae85259 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 b798932fa..b3a520848 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 9b7c49f50..21108d0bf 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 05e532cda..b51ab1782 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