[PATCH] uml: fix off-by-one bug in VM file creation

Fix an off-by-one bug in temp file creation.  Seeking to the desired length
and writing a byte resulted in the file being one byte longer than expected.

Signed-off-by: Jeff Dike <jdike@addtoit.com>
Cc: Paolo 'Blaisorblade' Giarrusso <blaisorblade@yahoo.it>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

1 files changed, 5 insertions, 2 deletions

diff --git a/arch/um/os-Linux/mem.c b/arch/um/os-Linux/mem.c
index d24d1a960523..560c8063c77c 100644
--- a/arch/um/os-Linux/mem.c
+++ b/arch/um/os-Linux/mem.c
@@ -210,8 +210,11 @@ int create_tmp_file(unsigned long long len)
                 exit(1);
         }
 
-        if (lseek64(fd, len, SEEK_SET) < 0) {
-                perror("os_seek_file");
+        /* Seek to len - 1 because writing a character there will
+         * increase the file size by one byte, to the desired length.
+         */
+        if (lseek64(fd, len - 1, SEEK_SET) < 0) {
+                perror("os_seek_file");
                 exit(1);
         }