Re: tree corrupted on disk quota full

From: Linus Torvalds <torvalds@osdl.org>
Date: Jan 11, 2007, 21:59 UTC
Message-ID: <Pine.LNX.4.64.0701111353030.3594@woody.osdl.org>
In-Reply-To: <45A6A97F.5080008@shadowen.org>

On Thu, 11 Jan 2007, Andy Whitcroft wrote:

Show 5 quoted lines

> 
> The call was intended to replace a common idiom:
> 
> if (xwrite(fd, buf, size) != size)
> 	error

I really don't agree.

You should use "write_or_die()" for this idiom.

There really is two cases:
 - the complex and robust one: "we will keep writing even in the presense 
   of partial writes".

   This is "xwrite()".

 - the simple case: "write everything", anything else is an error. This is 
   "write_or_die()", or "write_in_full()".

And I claim, that for the "write_in_full()" case, if you EVER get anything but the full length back, that's an error.

And it should be treated as such. There is NO POINT in write_in_full() ever returning a partial result. It's unrecoverable by design - and if it wasn't, you wouldn't use "write_in_full()" in the first place, you'd just use "xwrite()".

And returning a partial result in that case is just a recipe for disaster. I already pointed to one real bug due to this: write_buffer() was (and currently is) simply buggy. And it's buggy EXACTLY becaue "write_in_full()" was doing the wrong thing, and just made it easy to write buggy code - it was no easier to use than xwrite(), and thus there was no point to it. Might as well have just used xwrite() in the first place.

So I repeat: either you use "xwrite()" (and handle the partial case), or you use "write_in_full()" (and the partial case is an *ERROR*). There is no sane middle ground in between those cases.

			Linus