mmp: don't use O_RDWR in ext2fs_mmp_read

It doesn't seem to be necessary since ext2fs_mmp_write doesn't write
via mmp_fd, and opening the block device with O_RDWR will trigger
udev.

Triggering udev is bad because it leads to an infinite loop when
running dumpe2fs in response to a udev event.

[ Rebased onto the maint branch, and added O_RDONLY flag.  From the
  open(2) man page: "The argument flags must include one of the
  following access modes: O_RDONLY, O_WRONLY, or O_RDWR." -- TYT ]

Signed-off-by: Theodore Ts'o <tytso@mit.edu>

diff --git a/lib/ext2fs/mmp.c b/lib/ext2fs/mmp.c
index 9ef4580..7970aac 100644 (file)
--- a/lib/ext2fs/mmp.c
+++ b/lib/ext2fs/mmp.c
@@ -58,7 +58,7 @@ errcode_t ext2fs_mmp_read(ext2_filsys fs, blk64_t mmp_blk, void *buf)
         * the MMP block by the io_manager or the VM.  It needs to be fresh. */
        if (fs->mmp_fd <= 0) {
                struct stat st;
-               int flags = O_RDWR | O_DIRECT;
+               int flags = O_RDONLY | O_DIRECT;
 
                /*
                 * There is no reason for using O_DIRECT if we're working with