linux-kernel - RE: [PATCH 2/2] procfs: Add 'path' to /proc/<pid>/fdinfo/

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Date:   Wed, 1 Jun 2022 15:40:31 +0000
From:   David Laight <David.Laight@...LAB.COM>
To:     'Kalesh Singh' <kaleshsingh@...gle.com>,
        Stephen Brennan <stephen.s.brennan@...cle.com>
CC:     Ioannis Ilkos <ilkos@...gle.com>,
        "T.J. Mercier" <tjmercier@...gle.com>,
        Suren Baghdasaryan <surenb@...gle.com>,
        "Cc: Android Kernel" <kernel-team@...roid.com>,
        Jonathan Corbet <corbet@....net>,
        Sumit Semwal <sumit.semwal@...aro.org>,
        Christian König <christian.koenig@....com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        "David Hildenbrand" <david@...hat.com>,
        Christoph Anton Mitterer <mail@...istoph.anton.mitterer.name>,
        Johannes Weiner <hannes@...xchg.org>,
        Colin Cross <ccross@...gle.com>,
        Mike Rapoport <rppt@...nel.org>,
        "Paul Gortmaker" <paul.gortmaker@...driver.com>,
        Randy Dunlap <rdunlap@...radead.org>,
        LKML <linux-kernel@...r.kernel.org>,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        "open list:DOCUMENTATION" <linux-doc@...r.kernel.org>,
        Linux Media Mailing List <linux-media@...r.kernel.org>,
        DRI mailing list <dri-devel@...ts.freedesktop.org>,
        "moderated list:DMA BUFFER SHARING FRAMEWORK" 
        <linaro-mm-sig@...ts.linaro.org>
Subject: RE: [PATCH 2/2] procfs: Add 'path' to /proc/<pid>/fdinfo/

From: Kalesh Singh
> Sent: 31 May 2022 23:30
...
> > File paths can contain fun characters like newlines or colons, which
> > could make parsing out filenames in this text file... fun. How would your
> > userspace parsing logic handle "/home/stephen/filename\nsize:\t4096"? The
> > readlink(2) API makes that easy already.
> 
> I think since we have escaped the "\n" (seq_file_path(m, file, "\n")),
> then user space might parse this line like:
> 
> if (strncmp(line, "path:\t", 6) == 0)
>         char* path = line + 6;

The real annoyance is other things doing scans of the filesystem
that accidentally 'bump into' strange names.

While anything serious probably gets it right how many times
Do you run 'find' to quickly search for something?

Spaces in filenames (popularised by some other os) are a PITA.
Not to mention leading and trailing spaces!
Anyone using filenames that only contain spaces does need shooting.

Deliberately adding non-printables isn't really a good idea.

	David

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