From: Adhemerval Zanella <adhemerval.zanella@linaro.org>
To: Paul Eggert <eggert@cs.ucla.edu>, libc-alpha@sourceware.org
Cc: Xiaoming Ni <nixiaoming@huawei.com>
Subject: Re: [PATCH 3/3] linux: Optimize realpath stack usage
Date: Tue, 11 Aug 2020 12:18:27 -0300 [thread overview]
Message-ID: <637a27b3-96c6-5312-8df6-c476249bf084@linaro.org> (raw)
In-Reply-To: <0bc2bde9-c0e3-7465-fd18-c47862cc5150@linaro.org>
On 11/08/2020 11:14, Adhemerval Zanella wrote:
>
>
> On 10/08/2020 18:25, Paul Eggert wrote:
>> On 8/10/20 1:48 PM, Adhemerval Zanella wrote:
>>
>>> Regarding syscalls usage, for a sucessful path without symlinks it
>>> trades 2 syscalls (getcwd/lstat) for 5 (openat, readlink, fstat, stat,
>>> and close).
>>
>> Thanks for looking into this.
>>
>> There's no need for the new __resolve_path function to call __lstat64. It does that only to determine whether the file is a symlink or a directory, and it can do the former with __readlink (which it's gonna do already) and the latter by going into the next iteration and seeing whether it gets NOTDIR. Avoiding __lstat64 means we don't have to worry about irrelevant EOVERFLOW hassles.
>
> I am not sure we can skip the __lstat64 because we can't check if a subpath
> passed on __readlink is a directory or not (so we can move to next iteration
> in some cases).
>
> For instance the test 30 from stdlib/test-canon.c which issues:
>
> realpath ("./doesExist/someFile/", ...)
And I just checked your patch on BZ#24970 and it shows the issues:
$ grep ^FAIL stdlib/subdir-tests.sum
FAIL: stdlib/test-canon
$ cat stdlib/test-canon.out
/home/azanella/Projects/glibc/build/x86_64-linux-gnu/stdlib/test-canon: flunked test 30 (expected `NULL', got `/home/azanella/Projects/glibc/build/x86_64-linux-gnu/stdlib/doesExist/someFile')
/home/azanella/Projects/glibc/build/x86_64-linux-gnu/stdlib/test-canon: flunked test 31 (expected `NULL', got `/home/azanella/Projects/glibc/build/x86_64-linux-gnu/stdlib/doesExist')
2 errors.
I couldn't figure out a way to have the expected realpath semantic by
just using readlink.
next prev parent reply other threads:[~2020-08-11 15:18 UTC|newest]
Thread overview: 26+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-08-10 20:48 [PATCH 1/3] stdlib: Use fixed buffer size for realpath (BZ #26241) Adhemerval Zanella
2020-08-10 20:48 ` [PATCH 2/3] stdlib: Enforce PATH_MAX on allocated realpath buffer Adhemerval Zanella
2020-08-11 8:26 ` Florian Weimer
2020-08-11 9:54 ` Andreas Schwab
2020-08-11 10:24 ` Florian Weimer
2020-08-11 15:05 ` Adhemerval Zanella
2020-08-11 15:37 ` Paul Eggert
2020-08-11 18:29 ` Florian Weimer
2020-08-11 9:48 ` Andreas Schwab
2020-08-10 20:48 ` [PATCH 3/3] linux: Optimize realpath stack usage Adhemerval Zanella
2020-08-10 21:25 ` Paul Eggert
2020-08-11 14:14 ` Adhemerval Zanella
2020-08-11 15:18 ` Adhemerval Zanella [this message]
2020-08-11 15:52 ` Paul Eggert
2020-08-11 19:01 ` Adhemerval Zanella
2020-08-11 16:46 ` Andreas Schwab
2020-08-17 14:00 ` Dmitry V. Levin
2020-08-17 15:13 ` Andreas Schwab
2020-08-17 16:17 ` Dmitry V. Levin
2020-08-11 9:46 ` Andreas Schwab
2020-08-11 0:32 ` [PATCH 1/3] stdlib: Use fixed buffer size for realpath (BZ #26241) Matt Turner
2020-08-11 3:00 ` Xiaoming Ni
2020-08-11 14:57 ` Adhemerval Zanella
2020-08-12 1:38 ` Xiaoming Ni
2020-08-12 23:04 ` Adhemerval Zanella
2020-08-13 20:29 ` Adhemerval Zanella
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