On Dec 17, 2018, at 9:45 PM, Theodore Y. Ts'o <tytso@xxxxxxx> wrote:
>
> On Mon, Dec 17, 2018 at 03:53:46PM -0700, Andreas Dilger wrote:
>>> +#define EXT4_IGET_NORMAL 1
>>> +#define EXT4_IGET_HANDLE 2
>>
>> It would be better to make this:
>>
>> enum ext4_iget_flags {
>> EXT4_IGET_RESERVED = 0x00, /* just guessing, see further below */
>> EXT4_IGET_NORMAL = 0x01,
>> EXT4_IGET_HANDLE = 0x02,
>> };
>>
>>> - inode = ext4_iget(sb, ino);
>>> + inode = ext4_iget(sb, ino, 0);
>>
>> What does "0" mean? It isn't in the list of EXT4_IGET_* flags.
>> I'm guessing it means that access to reserved or otherwise invalid
>> inodes is allowed?
>
> The flags are boolean OR'ed together, much like O_TRUNC | O_CREAT,
> etc. So an enum isn't really appropriate.
I don't think that it is verboten to use binary flag values in an enum,
if you explicitly specify the values, which is why I used "0x01", "0x02"
to make it more clear these are binary values. IMHO, using a named enum
is a good way to annotate the function parameters rather than a generic
"int flag" parameter that is ambiguous unless you look at the function
code to see what the values of "flag" might be.
> So 0 means we're not enforcing "must be a normal inode" rules, and
> we're also not going to avoid throwing an EXT4_ERROR if the inode
> number is invalid.
So that matches what I reverse engineered, which was EXT4_IGET_RESERVED
but might have a better name if you can think of it. I originally had
EXT4_IGET_NONE = 0, but I don't think that is quite correct.
> I had thought it was obvious that flags can be or'ed together, and
> that "modes" are what might use an enum.
Their definition as "1" and "2" didn't make it clear that the next
possible value was "4" and not "3".
> I personally like flags because the can be more expressive, although
> I can see that "modes" are simpler since there is a much smaller set
> of valid modes, and you don't have to worry about define what happens
> when flags interact in unusual/unexpected ways.
I'm not against flags, and I figured out that they were orthogonal
flags after reading the whole patch.
> It sounds like should add more explicit documentation at the very
> least so it's more clear what's going on.
>
> - Ted
Cheers, Andreas
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