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

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