bug#67238: [PATCH] derivations: Avoid readlink syscalls in read-derivation-from-file.

[Christopher Baines <mail@cbaines.net>]

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Ludovic Courtès <ludo@gnu.org> writes:

> Hi,
>
> Christopher Baines <mail@cbaines.net> skribis:
>
>> strace -c reports over 10,000 readlink syscalls when reading the derivation
>> for the hello package. By just setting the %file-port-name-canonicalization
>> fluid, this drops to less than 10.
>>
>> I'm not sure if this actually improves performance, but doing less is surely
>> better.
>>
>> * guix/derivations.scm (read-derivation-from-file): Set
>> %file-port-name-canonicalization to 'none when calling call-with-input-file.
>>
>> Change-Id: I1ff16a059160576a576f2e9ed881379596e66af3
>
> [...]
>
>> +      (let ((drv
>> +             ;; Avoid calling scm_i_relativize_path in
>> +             ;; fport_canonicalize_filename since this leads to lots of
>> +             ;; readlink calls
>> +             (with-fluids ((%file-port-name-canonicalization 'none))
>> +               (call-with-input-file file read-derivation))))
>
> This is already done in ‘run-guix’ in (guix ui), for all the ‘guix’
> commands (so this patch would be a slight performance regression for
> Guix itself).
>
> I’d suggest setting this fluid globally in applications that use Guix
> (the Build Coordinator, etc.), as is done in Guix itself.
>
> WDYT?

Ah, I didn't realise it was already set for Guix scripts. But yeah,
setting it in other places that read derivations makes sense.

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