Re: [PATCH v3 0/8] Fix GIT_CEILING_DIRECTORIES that contain symlinks

From: Michael Haggerty <mhagger@alum.mit.edu>
Date: Oct 22, 2012, 08:26 UTC
Message-ID: <5085033E.2070607@alum.mit.edu>
In-Reply-To: <7v7gqkgvxe.fsf@alter.siamese.dyndns.org>

On 10/21/2012 08:51 AM, Junio C Hamano wrote:

Show 15 quoted lines

> Michael Haggerty <mhagger@alum.mit.edu> writes:
> 
>> This patch series has the side effect that all of the directories
>> listed in GIT_CEILING_DIRECTORIES are accessed *unconditionally* to
>> resolve any symlinks that are present in their paths.  It is
>> admittedly odd that a feature intended to avoid accessing expensive
>> directories would now *intentionally* access directories near the
>> expensive ones.  In the above scenario this shouldn't be a problem,
>> because /home would be the directory listed in
>> GIT_CEILING_DIRECTORIES, and accessing /home itself shouldn't be
>> expensive.
> 
> Interesting observation.  In the last sentence, "accessing /home"
> does not exactly mean accessing /home, but accessing / to learn
> about "home" in it, no?

This is the extra overhead on my system for using GIT_CEILING_DIRECTORIES=/home:

stat("/home", {st_mode=S_IFDIR|0755, st_size=4096, ...}) = 0 getcwd("/home/mhagger", 1024) = 14 chdir("/home") = 0 getcwd("/home", 4096) = 6 lstat("/home", {st_mode=S_IFDIR|0755, st_size=4096, ...}) = 0 chdir("/home/mhagger") = 0

If I use GIT_CEILING_DIRECTORIES=/dev/shm, which is a symlink to /run/shm on my system, the overhead is comparable:

stat("/dev/shm", {st_mode=S_IFDIR|S_ISVTX|0777, st_size=200, ...}) = 0 getcwd("/home/mhagger", 1024) = 14 chdir("/dev/shm") = 0 getcwd("/run/shm", 4096) = 9 lstat("/run/shm", {st_mode=S_IFDIR|S_ISVTX|0777, st_size=200, ...}) = 0 chdir("/home/mhagger") = 0

Michael

-- 
Michael Haggerty
mhagger@alum.mit.edu
http://softwareswirl.blogspot.com/