On Thu, Jun 11, 2020 at 08:53:10AM +0900, Daeho Jeong wrote: > > > > > Using FMODE_WRITE is more proper for this case, since we're going to > > > > > modify the data. But I think mnt_want_write_file() is still required > > > > > to prevent the filesystem from freezing or something else. > > > > > > > > Right, the freezing check is actually still necessary. But getting > > > > write access > > > > to the mount is not necessary. I think you should use > > > > file_start_write() and > > > > file_end_write(), like vfs_write() does. > > > > I've checked this again. > > > > But I think mnt_want_write_file() looks better than the combination of > > checking FMODE_WRITE and file_start_write(), because > > mnt_want_write_file() handles all the things we need. > > It checks FMODE_WRITER, which is set in do_dentry_open() when > > FMODE_WRITE is already set, and does the stuff that file_start_write() > > is doing. This is why the other filesystem system calls use it. > > > > What do you think? > > Hmm, we still need FMODE_WRITE check. > But mnt_want_write_file() looks better, because it'll call > mnt_clone_write() internally, if the file is open for write already.
There's no need to get write access to the mount if you already have a writable fd. You just need file_start_write() for the freeze protection. Again, see vfs_write(). - Eric
