Re: "ls -l": Avoid unnecessary getxattr() overhead

[Pádraig Brady]

On 02/09/2012 09:17 PM, Sven Breuner wrote:
> Jim Meyering wrote on 02/09/2012 03:17 PM:
>> Pádraig Brady wrote:
>>> On 02/09/2012 11:32 AM, Jim Meyering wrote:
>>>> Technically, we could probably exempt all files on that device, but
>>>> ...
>>>
>>> So you avoid symlinks as they can point outside the device.
>>> Unfortunately so can bind mounts, so you probably have to key on device?
>>
>> Thanks.  That confirms my impression that my patch was not worthwhile:
>> It was buggy, too.
>>
>> I suppose we could use a little hash table, whose entries are
>> <dev_t device_number, bool getfilecon_required>  pairs.
>>
>> Or even a single static dev_t selinux_challenged_device,
>> that if equal to f->stat.st_dev, we can skip the *getfilecon call.
>> That should be good enough for most uses.
>>
>> Here's that simpler patch:
>>
>> diff --git a/src/ls.c b/src/ls.c
>> index f5cd37a..cb9f834 100644
>> [...]
> 
> 
> Just tried it out and the difference is very significant, as expected.
> (Test case with 61,441 files in a directory.)
> 
> Current git version without the patch...
> 
> $ time ~/tmp/ls-8.15.34-31eee -l >/dev/null
> 
> real    0m31.135s
> user    0m0.859s
> sys     0m4.276s
> 
> $ strace -c ~/tmp/ls-8.15.34-31eee -l >/dev/null
> % time     seconds  usecs/call     calls    errors syscall
> ------ ----------- ----------- --------- --------- ----------------
>  31.13    0.303648           5     61441           lstat
>  30.81    0.300585           5     61441     61441 getxattr
>  30.65    0.298937           5     61441           lgetxattr
>   7.17    0.069987         933        75           getdents
> [...]
> 
> Current git version patched...
> 
> $ time ~/tmp/ls-8.15.34-31eee_patched -l >/dev/null
> 
> real    0m21.254s
> user    0m0.565s
> sys     0m2.496s
> 
> $ strace -c ~/tmp/ls-8.15.34-31eee_patched -l >/dev/null
> % time     seconds  usecs/call     calls    errors syscall
> ------ ----------- ----------- --------- --------- ----------------
>  45.50    0.313386           5     61441           lstat
>  43.63    0.300524           5     61441     61441 getxattr
>  10.60    0.072986         973        75           getdents

So you're still getting all those errors.
Is that from file_has_acl() or cap_get_file()?
Oh it must be from file_has_acl() as you've
not specified --color. What is the errno in that case?

Note you can avoid the cap_get_file() calls at least,
that would be enabled with --color, by unsetting capability
coloring, which you can test by running the following
before your ls command.

eval $(dircolors | sed 's/ca[^:]*:/ca=:/')

cheers,
Pádraig.