losetup: use offset in warn_size() calculation

 # dd if=/dev/urandom of=dummy bs=513 count=1 2>/dev/null

 # losetup -f --show --offset 1 dummy
 /dev/loop0
 losetup: dummy: Warning: file does not fit into a 512-byte sector; the end of the file will be ignore

The warning is bogus as with offset the size of the file fits into
512-byte sector. Simple test that all is right:

 # dd if=dummy bs=1 skip=1 2>/dev/null | sha256sum - /dev/loop0
 da2ed0ade6ea518a802cd8a7a3c01c408ad8699ef6856b0b01f92b867d4ba9b5  -
 da2ed0ade6ea518a802cd8a7a3c01c408ad8699ef6856b0b01f92b867d4ba9b5  /dev/loop0

Addresses: https://github.com/karelzak/util-linux/issues/722
Signed-off-by: Karel Zak <kzak@redhat.com>

1 files changed, 5 insertions, 2 deletions

diff --git a/sys-utils/losetup.c b/sys-utils/losetup.c
index 7d14f566c..db7b68deb 100644
--- a/sys-utils/losetup.c
+++ b/sys-utils/losetup.c
@@ -447,7 +447,7 @@ static void __attribute__((__noreturn__)) usage(void)
 	exit(EXIT_SUCCESS);
 }
 
-static void warn_size(const char *filename, uint64_t size)
+static void warn_size(const char *filename, uint64_t size, uint64_t offset, int flags)
 {
 	struct stat st;
 
@@ -455,6 +455,9 @@ static void warn_size(const char *filename, uint64_t size)
 		if (stat(filename, &st) || S_ISBLK(st.st_mode))
 			return;
 		size = st.st_size;
+
+		if (flags & LOOPDEV_FL_OFFSET)
+			size -= offset;
 	}
 
 	if (size < 512)
@@ -835,7 +838,7 @@ int main(int argc, char **argv)
 		if (res == 0) {
 			if (showdev)
 				printf("%s\n", loopcxt_get_device(&lc));
-			warn_size(file, sizelimit);
+			warn_size(file, sizelimit, offset, flags);
 			if (set_dio || set_blocksize)
 				goto lo_set_post;
 		}