losetup: implement -c

function                                             old     new   delta
losetup_main                                         422     449     +27
packed_usage                                       33243   33264     +21
get_next_block                                      1677    1681      +4
------------------------------------------------------------------------------
(add/remove: 0/0 grow/shrink: 3/0 up/down: 52/0)               Total: 52 bytes

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

1 files changed, 22 insertions, 10 deletions

diff --git a/util-linux/losetup.c b/util-linux/losetup.c
index bf480e9bf..2248f2cba 100644
--- a/util-linux/losetup.c
+++ b/util-linux/losetup.c
@@ -20,10 +20,11 @@
 //kbuild:lib-$(CONFIG_LOSETUP) += losetup.o
 
 //usage:#define losetup_trivial_usage
-//usage:       "[-r] [-o OFS] {-f|LOOPDEV} FILE - associate loop devices\n"
-//usage:       "        losetup -d LOOPDEV - disassociate\n"
-//usage:       "        losetup -a - show status\n"
-//usage:       "        losetup -f - show next free loop device"
+//usage:       "[-r] [-o OFS] {-f|LOOPDEV} FILE: associate loop devices\n"
+//usage:       "        losetup -c LOOPDEV: reread file size\n"
+//usage:       "        losetup -d LOOPDEV: disassociate\n"
+//usage:       "        losetup -a: show status\n"
+//usage:       "        losetup -f: show next free loop device"
 //usage:#define losetup_full_usage "\n\n"
 //usage:       "        -o OFS  Start OFS bytes into FILE"
 //usage:     "\n        -r      Read-only"
@@ -50,14 +51,15 @@ int losetup_main(int argc UNUSED_PARAM, char **argv)
         char *opt_o;
         char dev[LOOP_NAMESIZE];
         enum {
-                OPT_d = (1 << 0),
-                OPT_o = (1 << 1),
-                OPT_f = (1 << 2),
-                OPT_a = (1 << 3),
-                OPT_r = (1 << 4), /* must be last */
+                OPT_c = (1 << 0),
+                OPT_d = (1 << 1),
+                OPT_o = (1 << 2),
+                OPT_f = (1 << 3),
+                OPT_a = (1 << 4),
+                OPT_r = (1 << 5),
         };
 
-        opt = getopt32(argv, "^" "do:far" "\0" "?2:d--ofar:a--ofr", &opt_o);
+        opt = getopt32(argv, "^" "cdo:far" "\0" "?2:d--ofar:a--ofr", &opt_o);
         argv += optind;
 
         /* LOOPDEV */
@@ -73,6 +75,16 @@ int losetup_main(int argc UNUSED_PARAM, char **argv)
                 return EXIT_SUCCESS;
         }
 
+        /* -c LOOPDEV */
+        if (opt == OPT_c && argv[0]) {
+                int fd = xopen(argv[0], O_RDONLY);
+#ifndef LOOP_SET_CAPACITY
+# define LOOP_SET_CAPACITY 0x4C07
+#endif
+                xioctl(fd, LOOP_SET_CAPACITY, /*ignored:*/0);
+                return EXIT_SUCCESS;
+        }
+
         /* -d LOOPDEV */
         if (opt == OPT_d && argv[0]) {
                 if (del_loop(argv[0]))