losetup: support -f (Loic Grenie <loic.grenie@gmail.com>)

function                                             old     new   delta
losetup_main                                         238     278     +40
packed_usage                                       23021   23027      +6
------------------------------------------------------------------------------
(add/remove: 0/0 grow/shrink: 2/0 up/down: 46/0)               Total: 46 bytes

2 files changed, 45 insertions, 29 deletions

diff --git a/include/usage.h b/include/usage.h
index 09c8fa7d1..b028f5a5c 100644
--- a/include/usage.h
+++ b/include/usage.h
@@ -1868,19 +1868,21 @@
        "        -f      Output data as the log grows"
 
 #define losetup_trivial_usage \
-       "[-o OFFSET] [-d] LOOPDEVICE [FILE]]"
+       "[-o OFS] LOOPDEV FILE - associate loop devices\n" \
+       "        losetup -d LOOPDEV - disassociate\n" \
+       "        losetup [-f] - show"
 #define losetup_full_usage \
-       "(Dis)associate LOOPDEVICE with FILE, or display current associations" \
-       "\n\nOptions:\n" \
-       "        -d              Disassociate LOOPDEVICE\n" \
-       "        -o OFFSET       Start OFFSET bytes into FILE"
+       "Options:\n" \
+       "        -o OFS  Start OFS bytes into FILE\n" \
+       "        -f      Show first free loop device"
 #define losetup_notes_usage \
        "No arguments will display all current associations.\n" \
        "One argument (losetup /dev/loop1) will display the current association\n" \
        "(if any), or disassociate it (with -d). The display shows the offset\n" \
        "and filename of the file the loop device is currently bound to.\n\n" \
        "Two arguments (losetup /dev/loop1 file.img) create a new association,\n" \
-       "with an optional offset (-o 12345). Encryption is not yet supported.\n\n"
+       "with an optional offset (-o 12345). Encryption is not yet supported.\n" \
+       "losetup -f will show the first loop free loop device\n\n"
 
 #define ls_trivial_usage \
        "[-1Aa" USE_FEATURE_LS_TIMESTAMPS("c") "Cd" \
diff --git a/util-linux/losetup.c b/util-linux/losetup.c
index 9409cdff5..57e8569dc 100644
--- a/util-linux/losetup.c
+++ b/util-linux/losetup.c
@@ -14,54 +14,68 @@
 int losetup_main(int argc, char **argv);
 int losetup_main(int argc, char **argv)
 {
+        char dev[] = LOOP_NAME"0";
         unsigned opt;
         char *opt_o;
+        char *s;
         unsigned long long offset = 0;
 
-        opt = getopt32(argv, "do:", &opt_o);
+        /* max 2 args, all opts are mutially exclusive */
+        opt_complementary = "?2:d--of:o--df:f-do";
+        opt = getopt32(argv, "do:f", &opt_o);
         argc -= optind;
         argv += optind;
 
-        if (opt == 0x3) // -d + -o (illegal)
+        if (opt == 0x2) // -o
+                offset = xatoull(opt_o);
+
+        if (opt == 0x4 && argc) // -f does not take any argument
                 bb_show_usage();
 
         if (opt == 0x1) { // -d
                 /* detach takes exactly one argument */
                 if (argc != 1)
                         bb_show_usage();
-                if (!del_loop(argv[0]))
-                        return EXIT_SUCCESS;
-                bb_perror_nomsg_and_die();
+                if (del_loop(argv[0]))
+                        bb_perror_nomsg_and_die();
+                return EXIT_SUCCESS;
         }
 
-        if (opt == 0x2) // -o
-                offset = xatoull(opt_o);
-
-        /* -o or no option */
-
         if (argc == 2) {
+                /* -o or no option */
                 if (set_loop(&argv[0], argv[1], offset) < 0)
                         bb_perror_nomsg_and_die();
-        } else if (argc == 1) {
-                char *s = query_loop(argv[0]);
+                return EXIT_SUCCESS;
+        }
+
+        if (argc == 1) {
+                /* -o or no option */
+                s = query_loop(argv[0]);
                 if (!s)
                         bb_perror_nomsg_and_die();
                 printf("%s: %s\n", argv[0], s);
                 if (ENABLE_FEATURE_CLEAN_UP)
                         free(s);
-        } else {
-                char dev[sizeof(LOOP_NAME"0")] = LOOP_NAME"0";
-                char c;
-                for (c = '0'; c <= '9'; ++c) {
-                        char *s;
-                        dev[sizeof(LOOP_NAME"0")-2] = c;
-                        s = query_loop(dev);
-                        if (s) {
-                                printf("%s: %s\n", dev, s);
-                                if (ENABLE_FEATURE_CLEAN_UP)
-                                        free(s);
+                return EXIT_SUCCESS;
+        }
+
+        /* -o, -f or no option */
+        while (1) {
+                s = query_loop(dev);
+                if (!s) {
+                        if (opt == 0x4) {
+                                printf("%s\n", dev);
+                                return EXIT_SUCCESS;
                         }
+                } else {
+                        if (opt != 0x4)
+                                printf("%s: %s\n", dev, s);
+                        if (ENABLE_FEATURE_CLEAN_UP)
+                                free(s);
                 }
+
+                if (++dev[sizeof(dev) - 2] > '9')
+                        break;
         }
         return EXIT_SUCCESS;
 }