Date: Thu, 02 Aug 2012 19:52:11 +0800 From: David Xu <listlog2011@gmail.com> To: Konstantin Belousov <kostikbel@gmail.com> Cc: arch@freebsd.org, David Xu <davidxu@freebsd.org> Subject: Re: short read/write and error code Message-ID: <501A69EB.9000701@gmail.com> In-Reply-To: <20120802100240.GV2676@deviant.kiev.zoral.com.ua> References: <5018992C.8000207@freebsd.org> <20120801071934.GJ2676@deviant.kiev.zoral.com.ua> <20120801183240.K1291@besplex.bde.org> <20120801162836.GO2676@deviant.kiev.zoral.com.ua> <20120802040542.G2978@besplex.bde.org> <20120802100240.GV2676@deviant.kiev.zoral.com.ua>
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On 2012/8/2 18:02, Konstantin Belousov wrote:
> diff --git a/sys/kern/sys_pipe.c b/sys/kern/sys_pipe.c
> index 338256c..1a61b93 100644
> --- a/sys/kern/sys_pipe.c
> +++ b/sys/kern/sys_pipe.c
> @@ -1286,13 +1286,13 @@ pipe_write(fp, uio, active_cred, flags, td)
> }
>
> /*
> - * Don't return EPIPE if I/O was successful
> + * Don't return EPIPE if any byte was written.
> + * EINTR and other interrupts are handled by generic I/O layer.
> + * Do not pretend that I/O succeeded for obvious user error
> + * like EFAULT.
> */
> - if ((wpipe->pipe_buffer.cnt == 0) &&
> - (uio->uio_resid == 0) &&
> - (error == EPIPE)) {
> + if (uio->uio_resid != orig_resid && error == EPIPE)
> error = 0;
> - }
>
> if (error == 0)
> vfs_timestamp(&wpipe->pipe_mtime);
I dislike the patch, if I thought it is right, I would have already
submit such
a patch. Now let us see why your patch is wore than my version (attached):
-current:
short write is done, some bytes were sent
dofilewrite returns -1, errno is EPIPE
dofilewrite sends SIGPIPE
application is killed by SIGPIPE
-my attached version:
short write is done, some bytes were sent
dofilewrite return number of bytes sent, errno is zero
dofilewrite sends SIGPIPE.
application is killed by SIGPIPE
-you version:
short write is done, some bytes were sent.
dofilewrite returns number of bytes sent, errno is zero.
dofilewrite does not send SIGPIPE signal
application is not killed
application does not check return value from write()
application thinks it is successful, application does other things,
application might begin a bank account transaction.
...
application never comes back...
my patch is more compatible with -current. if application does not
setup a signal handler for SIGPIPE, when short write happens, it is killed,
it is same as -current. if the application set up a signal handler for
the signal,
it always should check the return value from write(), this is how
traditional
code works.
in your patch, short write does not kill application, you can not assume
that the application will request a next write() on the pipe, and you hope
the second write to kill the application, but there is always exception,
the next write does not happen, application works on other things.
This is too incompatible with -current.
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