[physfs] [patch] Do not fsync read-only file descriptors on Posix

[Andreas Karlsson]

Hi,

When debugging why a game was slow at starting on Linux I noticed that 
most of the time was spent in fsync calls from PhysicsFS. This was due 
to fsync calls on files opened with O_RDONLY causing flushes to disk of 
the access time changes (atime). See this forum thread for details of my 
debugging.[1] In most modern Linux distros relatime makes sure access 
times are only updated once, but not all Posix OSes has relatime and a 
slow first startup is not something good anyway.

The Windows version of __PHYSFS_platformFlush already checks if the file 
is opened read-only or not (presumably to solve the same problem) so I 
just added the equivalent check to the Posix version.

I have attached two patches, one against stable-2.0 and one against default.

Best regards,
Andreas

Footnotes
---

1. 
http://forum.paradoxplaza.com/forum/showthread.php?709094-Slow-game-startup-on-Linux-and-what-tracing-reveals

-- 
Andreas Karlsson
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