linux-kernel - Re: [RESEND PATCH v7 7/8] kernfs: Replace per-fs rwsem with hashed rwsems.

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Date:   Mon, 28 Mar 2022 11:15:30 +1100
From:   Imran Khan <imran.f.khan@...cle.com>
To:     Al Viro <viro@...iv.linux.org.uk>, Tejun Heo <tj@...nel.org>
Cc:     gregkh@...uxfoundation.org, linux-kernel@...r.kernel.org
Subject: Re: [RESEND PATCH v7 7/8] kernfs: Replace per-fs rwsem with hashed
 rwsems.

Hello Al,

On 22/3/22 1:40 pm, Al Viro wrote:
[...]
> 
> Sorry, misread that thing - the reason it copies the damn thing at all is
> the use of strsep().  Yecch...  Rule of the thumb regarding strsep() use,
> be it in kernel or in the userland: don't.  It's almost never the right
> primitive to use.
> 
> Lookups should use qstr; it has both the length and place for hash.
> Switch kernfs_find_ns() to that (and lift the calculation of length
> into the callers that do not have it - note that kernfs_iop_lookup()
> does) and you don't need the strsep() shite (or copying) anymore.
> 

Regarding using qstr in kernfs_find_ns, do you mean that I should remove
->name and ->hash with a ->qstr in kernfs_node and further modify
kernfs_name_compare to make use of qstr.name and qstr.hash.

Also the suggestion about removing buffer copying from kernfs_walk_ns is
not clear to me because kernfs_walk_ns invokes kernfs_find_ns with
individual path components so we need some mechanism to separate path
components.

Sorry if I have missed or misunderstood something in your suggestion.

Thanks,
-- Imran