Re: [Pfspd-users@sf.net] Linux, cygwin, and different yuv file sizes

[Bram R. <bra...@ph...>]

Hi Erwin, others,

Here my thoughts on the implementation of file size truncation on windows.

Currently, files are closed by function p_close_idx() in module 
cpfspd_low.
Possible reasons to close a file are:
- application request
- application opens new file while many files already open (least recently 
used file is closed)
- atexit function when application terminates

Main issue: the file header info is required in order to calculate the 
file size.
This info is not available in p_close_idx(). In many cases,
this info is not even in the application anymore.

Note that p_close_idx() already writes the number of images at the
beginning of the file (hence, it adapts the file header) in case
the actual file contains more images than the data in the file header.

Simple approach

The win32 api has calls to set file size. Maybe this works for files
opened unbuffered and asynchronously. If this is true, then this
simple approach will work.

Therefore, the approach must be:
- move to beginning of the file
- read the header
- calculate file length
- set file length
- close file

Extended approach

It may be required to close the file first, then reopen it in normal mode.
This results in a slightly more extended approach:
- perform regular close of the file
- reopen the file (normal mode)
- read the header
- calculate file length
- set file length
- close file

Other notes

Module cpfspd_low.
- Add required functionality in p_close_idx().
- File size calculation is analogous to file positioning when accessing an 
image,
  see e.g. cpfspd_low.c function p_read_image() lines 1593-1610.

Some win API background info for use in cpfspd_fio:
- OpenFile() 
http://msdn.microsoft.com/library/default.asp?url=/library/en-us/fileio/fs/openfile.asp
- ReOpenFile() 
http://msdn.microsoft.com/library/default.asp?url=/library/en-us/fileio/fs/reopenfile.asp
- SetFilePointer() 
http://msdn.microsoft.com/library/default.asp?url=/library/en-us/fileio/fs/setfilepointer.asp
- SetEndOfFile() 
http://msdn.microsoft.com/library/default.asp?url=/library/en-us/fileio/fs/setendoffile.asp
- CloseHandle() 
http://msdn.microsoft.com/library/default.asp?url=/library/en-us/sysinfo/base/closehandle.asp
Examples of most of these calls are already in cpfspd_fio.c
I expect, when reopening the file in the new mode, all regular file access 
works as expected.
Hence, first reopen the file in normal buffered mode; then perform the 
regular p_read_header()
(which uses fio_read functions) will work as usual.
I expect, only new code is to be added. No existing code needs 
modification.

Regards, Bram.

--
A.K. (Bram) Riemens
Principal Scientist, DSP group, Philips Research
Office: WO-p-94, Postbox WO02
High Tech Campus 36 (WO), 5656 AE Eindhoven, The Netherlands
Tel: +31 40 27 43833, Fax: +31 40 27 44675
E-mail: bra...@ph...








Erwin de Kock
30-01-2006 21:15

To
Bram Riemens/EHV/RESEARCH/PHILIPS@PHILIPS
cc

Subject
Re: [Pfs...@sf...] Linux, cygwin, and different yuv file  sizes
Classification
Unclassified





Hi Bram,

Thanks for the response. I am using your software in our open source 
project at http://sourceforge.net/projects/y-api. The internal tool pts is 
not available for the general public so I prefer your suggestion to adapt 
the file size when closing the file. Then I can check against expected 
output using "diff -q". I am willing to help with this change, but I have 
to familiarize myself with your code. I will contact you if I have 
questions :)

Best regards,
--Erwin