Re: BUG in fs/proc/generic.c:proc_file_read

[Zwane Mwaikambo]

On Thu, 7 Aug 2003, Nagendra Singh Tomar wrote:

> In short:
> The hack used to be able to read proc files larger than 4k, breaks if the 
> caller does lseek() after read()
> 
> Detailed:
> I am providing a proc read interface to one of my proc files by using the 
> given hack symantics in which every call to read_proc() writes the data 
> starting at the begining of the page but sets "*start" artificially to 
> indicate how many fields have been read. proc_file_read then correctly 
> adjusts *ppos to signify the artificial position inside the proc file 
> where the read pointer points. It is *artificial* beacuse it is not the 
> byte offset but some other offset which only read_proc understands. Next 
> time around when read_proc gets the *ppos to start reading from it knows 
> how to calculate the exxat byte offset from the *artificial* *ppos 
> provided.
> This works fine with cat which simply calls read(). The "more" command 
> though has the following call pattern
> 
> read(fd,buf,4096) = X
> lseek(fd,X,SEEK_SET);
> 
> -- lseek modified file->f_pos to the byte offset value, which disturbed 
> read_proc ---
> 
> read(fd,buf,4096) = 0;
> 
> 
> the effect is that more never gives me data more than 4096 bytes worth.
> 
> My Question is. Is it a known problem ? 

Yep known issue, i need to get around to look and test the patch.

http://bugzilla.kernel.org/show_bug.cgi?id=952

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