Re: [PATCH 1/1] UML: fix missing non-blocking I/O, now DEBUG_SHIRQ works

From: Jeff Dike
Date: Mon Jun 11 2007 - 20:48:25 EST

On Tue, Jun 12, 2007 at 01:39:25AM +0300, Eduard-Gabriel Munteanu wrote:
> The cast isn't done right. Doing "fd = (long) dev_id;" doesn't help,
> since you pass fd to mconsole_get_request() as is. And
> mconsole_get_request() expects an integer:
> int mconsole_get_request(int fd, struct mc_request *req)

gcc will trim a long to an integer correctly. You can pass a long to
an integer without casting.

> This will generate at least a warning on arches where sizeof(int) !=
> sizeof(long).

No it won't. UML builds without warnings here on x86_64.

> And by the way, AFAIK, GCC has the habit of breaking compatibility with
> some userspace apps when a new GCC major version is released. And,
> AFAIK, they're moving towards standards, so relying on GCC's
> "guarantees" may backfire.

The GCC guarantee I'm talking about it LP64 - I'm highly confident
that's not changing any time soon.

> >>You're calling glibc functions
> >>with that fd as a parameter. On some arches, compiling will issue
> >>warnings or simply fail.
> >
> >Which ones?
> >
> An example is sparc64:
> quote from
> >>

What warnings does this produce? These are the same sizes as x86_64
(and every other 64-bit arch that Linux runs on, I bet), where this
code compiles without warning.

> Really, a kmalloc() isn't such a big deal, it only happens once and
> we're not in interrupt context.

It's not the runtime cost - it's the extra code.

> One the other hand, ensuring safety and
> portability on other arches is something that needs to be taken care
> of.

You haven't demonstrated any safety or portability problems yet.


Work email - jdike at linux dot intel dot com
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