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Bug #39520 disk_free_space uses f_frsize but it should use f_bsize
Submitted: 2006-11-15 05:26 UTC Modified: 2006-11-16 15:47 UTC
From: david at triax dot jp Assigned:
Status: Not a bug Package: Filesystem function related
PHP Version: 5.2.0 OS: RedHat Enterprise ES 4
Private report: No CVE-ID: None
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 [2006-11-15 05:26 UTC] david at triax dot jp 
Description:
------------
Using disk_free_space() on an NFS mount produced incorrect results so checking with strace, it seems PHP is ignoring the value of f_bsize and either using f_frsize or just using a fixed blocksize of 4096. I haven't checked the source code yet. Calling stat() on the same path shows the correct blocksize for the filesystem, in my case 32768, and so dividing the output of disk_free_space() by 4096 and multiplying by the result of stat()'s blksize element.


Expected result:
----------------
I expected the value of disk_free_space() to use the same block size as reproted by stat() on the same path.

Actual result:
--------------
disk_free_space() seems to use a fixed 4096 byte block size.

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 [2006-11-15 09:53 UTC] tony2001@php.net 
No, you are wrong. See lines 365-369 here: http://cvs.php.net/viewvc.cgi/php-src/ext/standard/filestat.c?view=annotate
 [2006-11-15 11:35 UTC] david at triax dot jp 
As I wrote initially, it is either using f_frsize or just using a fixed blocksize and as you point out it's using f_frsize, and that is wrong. It should use f_bsize when calculating free space.
 [2006-11-16 03:41 UTC] david at triax dot jp 
This is not a bogus bug. Please reread.
 [2006-11-16 03:42 UTC] david at triax dot jp 
This is not a bogus bug. Please reread.
 [2006-11-16 03:46 UTC] david at triax dot jp 
Changed the subject to reflect the actual bug. From the stat(2) man page, fr_size is "the 'preferred' block-size for efficient file system I/O." This means that it's *not* the blocksize of the actual device and is not useful for calculating the size of the device.
 [2006-11-16 15:47 UTC] iliaa@php.net 
I've checked the current behavior against other applications 
and utilities that calculate free disk space and PHP's 
approach is perfectly inline with what other people are doing.
 
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