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SubjectRe: [PATCH v7 08/24] erofs: add namei functions
Hi Pavel,

On Tue, Aug 13, 2019 at 01:48:21PM +0200, Pavel Machek wrote:
> Hi!
>
> > + /*
> > + * on-disk error, let's only BUG_ON in the debugging mode.
> > + * otherwise, it will return 1 to just skip the invalid name
> > + * and go on (in consideration of the lookup performance).
> > + */
> > + DBG_BUGON(qd->name > qd->end);
>
> I believe you should check for errors in non-debug mode, too.

Thanks for your kindly reply!

The following is just my personal thought... If I am wrong, please
kindly point out...

As you can see, this is a new prefixed string binary search algorithm
which can provide similar performance with hashed approach (but no
need to store hash value at all), so I really care about its lookup
performance.

There is something needing to be concerned, is, whether namei() should
report any potential on-disk issues or just return -ENOENT for these
corrupted dirs, I think I tend to use the latter one.

The reason (in my opinion) is if you consider another some another
complicated non-transverse ondisk implementation, it cannot transverse
all the entires so they could/couldn't report all potential issues
in namei() (For such corrupted dir, they can return -ENOENT due
to lack of information of course, just avoiding crashing the kernel
is OK).

Therefore, in my thought, such issue can be reported by fsck-like
tools such as erofs.fsck. And actually readdir() will also report
all issues as well, thus we can have performance gain on lookup.

>
>
> > + if (unlikely(!ndirents)) {
> > + DBG_BUGON(1);
> > + kunmap_atomic(de);
> > + put_page(page);
> > + page = ERR_PTR(-EIO);
> > + goto out;
> > + }
>
> -EUCLEAN is right error code for corrupted filesystem. (And you
> probably want to print something to the syslog, too).

Yes, you are right :) -EUCLEAN/EFSCORRUPTED is actually for such thing,
nowadays, EROFS treats all EFSCORRUPTED cases into EIO, and I will
update that in one patch... (Yes, it needs to print something of course :))

Thanks,
Gao Xiang

>
> Pavel
> --
> DENX Software Engineering GmbH, Managing Director: Wolfgang Denk
> HRB 165235 Munich, Office: Kirchenstr.5, D-82194 Groebenzell, Germany


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