Messages in this thread | ![/](/images/icornerl.gif) | | Date | Thu, 7 Aug 2003 23:59:00 +0530 (IST) | From | Nagendra Singh Tomar <> | Subject | BUG in fs/proc/generic.c:proc_file_read |
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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 ?
Thanx tomar
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