Re: proc_file_read bug?

[Andreas Schwab]

Thomas Hood <[e-mail]> 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. - [e-mail]
|>                  */
|>                 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, [e-mail]
SuSE GmbH, Deutschherrnstr. 15-19, D-90429 Nürnberg
Key fingerprint = 58CA 54C7 6D53 942B 1756  01D3 44D5 214B 8276 4ED5
"And now for something completely different."