What is negative lookup in linux filesystem

What is negative lookup in linux filesystem

[Praveen Kumar]

Hi,

I am trying to understand the path-lookup in linux filesystem and was going
through https://www.kernel.org/doc/Documentation/filesystems/path-lookup.txt

Under 'Rename' heading, I came across the negative lookup terminology,
snapshot below

'Between deleting the dentry from the old hash list, and inserting it on
the new
hash list, a lookup may find neither 'A' nor 'B' matching the dentry. The
same
rename seqlock is also used to cover this race in much the same way, by
retrying a negative lookup result if a rename was in progress.'

Can anyone please help understanding the negative lookup concept and how do
we achieve it. Thanks in advance.

Regards,

~Praveen.
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What is negative lookup in linux filesystem

[Mandeep Sandhu]

>From the context of the snippet you posted, it looks like the author
implies a "failed lookup" when s/he writes "negative lookup".

CMIIW.

-mandeep



On Mon, Oct 5, 2015 at 8:08 AM, Praveen Kumar <kpraveen.lkml@gmail.com> wrote:
> Hi,
>
> I am trying to understand the path-lookup in linux filesystem and was going
> through https://www.kernel.org/doc/Documentation/filesystems/path-lookup.txt
>
> Under 'Rename' heading, I came across the negative lookup terminology,
> snapshot below
>
> 'Between deleting the dentry from the old hash list, and inserting it on the
> new
> hash list, a lookup may find neither 'A' nor 'B' matching the dentry. The
> same
> rename seqlock is also used to cover this race in much the same way, by
> retrying a negative lookup result if a rename was in progress.'
>
> Can anyone please help understanding the negative lookup concept and how do
> we achieve it. Thanks in advance.
>
> Regards,
>
> ~Praveen.
>
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