From 309f5e3775ed9cc0837c6d93482735bc4f117d5b Mon Sep 17 00:00:00 2001
From: Denys Vlasenko <vda.linux@googlemail.com>
Date: Thu, 23 May 2019 16:11:42 +0200
Subject: [PATCH] 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>
---
 util-linux/losetup.c | 32 ++++++++++++++++++++++----------
 1 file 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]))