ID: 43864
User updated by: sq6elt at wp dot pl
Reported By: sq6elt at wp dot pl
Status: Wont fix
Bug Type: Performance problem
Operating System: Linux
PHP Version: 5.2.5
New Comment:
>From logical point of view, these files are different.
Programmers should thread this as different files.
Besides, this is broken for hardlinks, only symlinks may be determined
by this call.
Simple test (rp.c)
#include <stdlib.h>
#include <string.h>
char x[4096];
int main(int argc, char* argv[]) {
if (argc != 2 ) {
printf("Provide a path %i\n", argc);
return 0;
}
memset(x, 0, 4096);
realpath(argv[1], x);
printf("Realpath for %s is %s\n", argv[1], x);
}
$ ./rp /home/ftp/welcome.msg
Realpath for /home/ftp/welcome.msg is /home/ftp/welcome.msg
$ mkdir /home/t
$ mount /home/ftp /home/t --bind
$ ./rp /home/t/welcome.msg
Realpath for /home/t/welcome.msg is /home/t/welcome.msg
So, this is partial solution, and in some environment
have big performance impacts.
If its really required to know if two files are really
the same file, look at stat.
$ stat /home/ftp/welcome.msg
File: `/home/ftp/welcome.msg'
Size: 166 Blocks: 8 IO Block: 4096 regular
file
Device: 807h/2055d Inode: 67117468 Links: 1
[...]
$ stat /home/t/welcome.msg
File: `/home/t/welcome.msg'
Size: 166 Blocks: 8 IO Block: 4096 regular
file
Device: 807h/2055d Inode: 67117468 Links: 1
[...]
One may determine if two files are really the same by comparing
device and inode.
This compare do a single stat on target file and not stats on each path
element, and solves hard linking.
Previous Comments:
------------------------------------------------------------------------
[2009-06-18 14:17:44] ras...@php.net
We need the realpath call to determine if there are symlinks in the
path. If /a is a symlink to /b and you do:
require '/a/file.php';
require_once '/b/file.php';
then file.php is actually the same file and the second require_once
should do nothing, but we can only know that with a realpath call.
In 5.3 we have replaced the system-level realpath call with our own
implementation which does intra-path caching, so this has been addressed
now, but it won't be changed in 5.2.
------------------------------------------------------------------------
[2009-06-18 09:35:34] sq6elt at wp dot pl
From: TSRM/tsrm_virtual_cwd.c
if (!realpath(path, resolved_path)) { /* Note: Not threadsafe on older
BSD's */
if (use_realpath == CWD_REALPATH) {
return 1;
}
goto no_realpath;
}
use_realpath = CWD_REALPATH;
CWD_STATE_COPY(&old_state, state);
Manual page says:
BUGS
Avoid using this function. It is broken by design...
So please avoid use this function, as stated above it has significant
performance impact and as stated in manual it's simply broken.
For now I have disabled this, by undefining HAVE_REALPATH.
------------------------------------------------------------------------
[2008-01-16 17:18:27] nlgordon at iastate dot edu
I've seen this same issue, and while I agree that it is excessive
considering the realpath cache. It appears to be a byproduct of using
realpath on pretty much all file accesses for includes.
Theoretically the realpath cache could be extended to cover directories
and the like. I know I would like it, my servers get hit hard because
I'm serving php out of AFS space.
------------------------------------------------------------------------
[2008-01-16 08:21:25] sq6elt at wp dot pl
Description:
------------
With a lot of includes, located deep in file system,
there may be a performance impact, because of a lot of
unnecessary lstats.
Why, when there is exactly specified path, any lstats are made.
Simple access is sufficient, or I missed something?
If some of these are required, then do it only once.
I have checked php4, it behaves in the same way.
There is no difference, when i use include, include_once, require,
require_once.
Reproduce code:
---------------
Create a directory tree:
mkdir -p /tmp/a/b/c/d/e/f/g/h/i/j
Two empty php scripts:
echo '<? ?>' > /tmp/a/b/c/d/e/f/g/h/i/j/a.php
echo '<? ?>' > /tmp/a/b/c/d/e/f/g/h/i/j/b.php
and a main script /tmp/t.php
<?
include "/tmp/a/b/c/d/e/f/g/h/i/j/a.php";
include "/tmp/a/b/c/d/e/f/g/h/i/j/b.php";
?>
Actual result:
--------------
Do a strace on t,php
strace /usr/bin/php5 t.php 2>&1 | grep lstat64
And guess what:
lstat64("/usr", {st_mode=S_IFDIR|0755, st_size=4096, ...}) = 0
lstat64("/usr/bin", {st_mode=S_IFDIR|0755, st_size=49152, ...}) = 0
lstat64("/usr/bin/php5", {st_mode=S_IFREG|0755, st_size=5510176, ...})
= 0
lstat64("/etc", {st_mode=S_IFDIR|0755, st_size=8192, ...}) = 0
lstat64("/etc/php5", {st_mode=S_IFDIR|0755, st_size=4096, ...}) = 0
lstat64("/etc/php5/cli", {st_mode=S_IFDIR|0755, st_size=4096, ...}) =
0
lstat64("/etc/php5/cli/php.ini", {st_mode=S_IFREG|0644, st_size=44278,
...}) = 0
lstat64("/tmp", {st_mode=S_IFDIR|S_ISVTX|0777, st_size=8192, ...}) = 0
lstat64("/tmp/t.php", {st_mode=S_IFREG|0644, st_size=94, ...}) = 0
lstat64("/tmp", {st_mode=S_IFDIR|S_ISVTX|0777, st_size=8192, ...}) = 0
lstat64("/tmp/a", {st_mode=S_IFDIR|0755, st_size=4096, ...}) = 0
lstat64("/tmp/a/b", {st_mode=S_IFDIR|0755, st_size=4096, ...}) = 0
lstat64("/tmp/a/b/c", {st_mode=S_IFDIR|0755, st_size=4096, ...}) = 0
lstat64("/tmp/a/b/c/d", {st_mode=S_IFDIR|0755, st_size=4096, ...}) = 0
lstat64("/tmp/a/b/c/d/e", {st_mode=S_IFDIR|0755, st_size=4096, ...}) =
0
lstat64("/tmp/a/b/c/d/e/f", {st_mode=S_IFDIR|0755, st_size=4096, ...})
= 0
lstat64("/tmp/a/b/c/d/e/f/g", {st_mode=S_IFDIR|0755, st_size=4096,
...}) = 0
lstat64("/tmp/a/b/c/d/e/f/g/h", {st_mode=S_IFDIR|0755, st_size=4096,
...}) = 0
lstat64("/tmp/a/b/c/d/e/f/g/h/i", {st_mode=S_IFDIR|0755, st_size=4096,
...}) = 0
lstat64("/tmp/a/b/c/d/e/f/g/h/i/j", {st_mode=S_IFDIR|0755,
st_size=4096, ...}) = 0
lstat64("/tmp/a/b/c/d/e/f/g/h/i/j/a.php", {st_mode=S_IFREG|0644,
st_size=11, ...}) = 0
lstat64("/tmp", {st_mode=S_IFDIR|S_ISVTX|0777, st_size=8192, ...}) = 0
lstat64("/tmp/a", {st_mode=S_IFDIR|0755, st_size=4096, ...}) = 0
lstat64("/tmp/a/b", {st_mode=S_IFDIR|0755, st_size=4096, ...}) = 0
lstat64("/tmp/a/b/c", {st_mode=S_IFDIR|0755, st_size=4096, ...}) = 0
lstat64("/tmp/a/b/c/d", {st_mode=S_IFDIR|0755, st_size=4096, ...}) = 0
lstat64("/tmp/a/b/c/d/e", {st_mode=S_IFDIR|0755, st_size=4096, ...}) =
0
lstat64("/tmp/a/b/c/d/e/f", {st_mode=S_IFDIR|0755, st_size=4096, ...})
= 0
lstat64("/tmp/a/b/c/d/e/f/g", {st_mode=S_IFDIR|0755, st_size=4096,
...}) = 0
lstat64("/tmp/a/b/c/d/e/f/g/h", {st_mode=S_IFDIR|0755, st_size=4096,
...}) = 0
lstat64("/tmp/a/b/c/d/e/f/g/h/i", {st_mode=S_IFDIR|0755, st_size=4096,
...}) = 0
lstat64("/tmp/a/b/c/d/e/f/g/h/i/j", {st_mode=S_IFDIR|0755,
st_size=4096, ...}) = 0
lstat64("/tmp/a/b/c/d/e/f/g/h/i/j/b.php", {st_mode=S_IFREG|0644,
st_size=7, ...}) = 0
------------------------------------------------------------------------
--
Edit this bug report at http://bugs.php.net/?id=43864&edit=1
