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Date:   Wed, 10 Jun 2020 18:56:51 -0700
From:   Eric Biggers <ebiggers@kernel.org>
To:     Daeho Jeong <daeho43@gmail.com>
Cc:     linux-kernel@vger.kernel.org,
        linux-f2fs-devel@lists.sourceforge.net, kernel-team@android.com,
        Daeho Jeong <daehojeong@google.com>
Subject: Re: [f2fs-dev] [PATCH] f2fs: add F2FS_IOC_SEC_TRIM_FILE ioctl
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On Thu, Jun 11, 2020 at 09:23:23AM +0900, Daeho Jeong wrote:
> Yes, I saw the implementation in vfs_write().
> But if we use mnt_want_write_file() here, it'll call mnt_clone_write()
> internally if the file is already open in write mode.
> Don't you think the below thing is needed? We can increase the counter
> each of them, open and ioctl, like other filesystems such as ext4.
> 
> int mnt_clone_write(struct vfsmount *mnt)
> {
>         /* superblock may be r/o */
>         if (__mnt_is_readonly(mnt))
>                 return -EROFS;
>         preempt_disable();
>         mnt_inc_writers(real_mount(mnt));
>         preempt_enable();
>         return 0;
> }

No, this seems to be left over from when mnt_want_write_file() was paired with
mnt_drop_write() instead of mnt_drop_write_file().  I sent a patch to remove it:
https://lkml.kernel.org/r/20200611014945.237210-1-ebiggers@kernel.org

- Eric