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From:   Daeho Jeong <daeho43@gmail.com>
Date:   Mon, 31 Aug 2020 12:55:27 +0900
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Subject: Re: [f2fs-dev] [PATCH] f2fs: prevent compressed file from being
 disabled after releasing cblocks
To:     Chao Yu <yuchao0@huawei.com>
Cc:     Chao Yu <chao@kernel.org>, Daeho Jeong <daehojeong@google.com>,
        kernel-team@android.com, linux-kernel@vger.kernel.org,
        linux-f2fs-devel@lists.sourceforge.net
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> - open(O_RDWR)
> - ioctl(FS_IOC_SETFLAGS, F2FS_COMPR_FL)
> - write()
> - ioctl(RELEASE_COMPRESS_BLOCKS) -- inode is immutable now
> - ioctl(FS_IOC_SETFLAGS, ~F2FS_COMPR_FL) -- Should we allow to update immutable inode?
> as we know, normally, immutable inode should deny open(O_WRONLY or O_RDWR) and later update.
>

For this case, with this patch we'll return -EINVAL for
ioctl(FS_IOC_SETFLAGS, ~F2FS_COMPR_FL).
I thought RESERVE_COMPRESS_BLOCKS ioctl is always required to get the
file to normal mode after RELEASE_COMPRESS_BLOCKS is called.