[OpenAFS-devel] dumpstuff.c buffering: 2 questions

[Peter Somogyi]

Hi,

I'm also involved in reading/writting a vnode, therefore I'm examining dumpstuff.c.
I've found the following code in src/volser/dumpstuff.c, function DumpFile:

static int
DumpFile(struct iod *iodp, int vnode, FdHandle_t * handleP)
{
...
	n = (lcode ? 0 : FDH_READ(handleP, p, howMany));
...
	/* If didn't read enough data, null padd the rest of the buffer. This
	 * can happen if, for instance, the media has some bad spots. We don't
	 * want to quit the dump, so we start null padding.
	 */
	if (n < howMany) {
...
	    memset(p + n, 0, howMany - n);
...
	}
...
	/* Now write the data out */
	if (iod_Write(iodp, (char *)p, howMany) != howMany)
	    error = VOLSERDUMPERROR;
...
}

I've examined FDH_READ implementation, it's a standard read.
I've read its manual (man 2 read), and it tells "[...]it is not an error if this number is smaller than the number of bytes requested; this may happen
       for example because fewer bytes are actually available right now (maybe because we were close to end-of-file,  or
       because  we  are  reading  from  a  pipe, or from a terminal)[...]".
So I think instead of null padding it should continue reading (if n>0, of course) - at least on Linux platform. Am I right?

Another question is about rx_Write(call, buf, nbytes): is it true that writting less (but >0) than nbytes means an error?
(in case of file write: it's also not an error)

Any feedback appreciated.

-- 
Peter Somogyi
Software Developer, Gamax Ltd.
1114 Budapest, Bartok B. u 15/d
Tel.: +36-1-381-0544
e-mail: psomogyi@gamax.hu