Re: proc_file_read bug?

From: Andreas Schwab (schwab@suse.de)
Date: Fri Jan 25 2002 - 09:29:35 EST


Thomas Hood <jdthood@mail.com> writes:

|> I don't understand this part of proc_file_read() in
|> fs/proc/generic.c:
|>
|> /* This is a hack to allow mangling of file pos independent
|> * of actual bytes read. Simply place the data at page,
|> * return the bytes, and set `start' to the desired offset
|> * as an unsigned int. - Paul.Russell@rustcorp.com.au
|> */
|> n -= copy_to_user(buf, start < page ? page : start, n);
|> if (n == 0) {
|> if (retval == 0)
|> retval = -EFAULT;
|> break;
|> }
|>
|> *ppos += start < page ? (long)start : n; /* Move down the file */
|> nbytes -= n;
|> buf += n;
|> retval += n;
|>
|> When start >= page, we copy n bytes beginning at start and
|> increase *ppos by n. Makes sense. But what happens when
|> start < page? We will copy n bytes starting at page, then
|> increase *ppos by start!! What sense does that make? If
|> there's cleverness happening here, someone please document it.

It is documented, RTFC.

Andreas.

-- 
Andreas Schwab, SuSE Labs, schwab@suse.de
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