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SubjectRe: [GIT PULL] ext4 updates for 4.15
On Tue, Nov 14, 2017 at 12:59:17PM -0800, Linus Torvalds wrote:
> Of course,
>
> (flags & EXT4_ENCRYPT_FL)
>
> _should_ be the same as
>
> ext4_test_inode_flag(inode, EXT4_INODE_ENCRYPT);

And in the second is the preferred way to do things, actually.

> I'll do that suggested resolution, but I have to say that the ext4 bit
> testing is incredibly broken and non-obvious. Just as an example:
>
> fs/ext4/ext4.h:#define EXT4_ENCRYPT_FL 0x00000800
> /* encrypted file */
> fs/ext4/ext4.h: EXT4_INODE_ENCRYPT = 11, /* Encrypted file */
>
> yeah, it's the same bit, but it sure as hell isn't obvious. Why the
> two totally different ways to define that data?

Yes, it's non-obvious and ugly. Sorry about that.

We originally used EXT4_*_FL, and we needed to use the bit number
encoding so we could use test_bit(). We just never converted all the
way over.

We do have a way to make sure the two ways of defining a bit position
are in sync; see ext4_check_flag_values() and CHECK_FLAG_VALUE in
ext4.h. It's a bit gross, and we probably should clean this up, at
least in the kernel. The e2fsprogs user space libraries all use
EXT4_*_FL, and we can't change that without breaking applications
depending on userspace, but we can keep things consistent in the
kernel, and that probably means completely converting away from
EXT4_*_FL, if possible.

- Ted

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