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Re: [Qemu-block] [PATCH 05/25] nbd: Avoid generic -EINVAL

From: Max Reitz
Subject: Re: [Qemu-block] [PATCH 05/25] nbd: Avoid generic -EINVAL
Date: Mon, 16 Mar 2015 10:48:07 -0400
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.5.0

On 2015-03-16 at 10:42, Paolo Bonzini wrote:

On 16/03/2015 14:51, Max Reitz wrote:
Propagating the return value from write_sync is uglier, but it is even
better in terms of returned value.
We can only return -errno values, but write_sync() may do partial writes
so it may return non-negative values which still indicate an error. So
we'd have to check whether the return value is negative, if it is,
return that, if it isn't but if it's still below what we wanted to
write, return a fixed error (such as -EIO). I'd rather just return -EIO
and be done with it, but if you really want me to, I can of course do it
nbd_wr_sync doesn't do that, it always returns negative errno for a partial

qemu_send() might do a partial send, returning a value smaller than len. nbd_wr_sync() will try iterating until everything has been sent, but if send() returns 0, the loop is aborted and a value smaller than len may be returned.

Maybe send() never returns 0, in which case nbd_wr_sync() will actually return either len or -errno, but this isn't clear from the structure of nbd_wr_sync(). If you really want to pass the value returned from nbd_wr_sync(), I'd rather restructure that function so that it always returns either len or -errno.


         if (len < 0) {
             err = socket_error();

             /* recoverable error */
             if (err == EINTR || (offset > 0 && (err == EAGAIN || err == 

             /* unrecoverable error */
             return -err;

The precise error can be useful to distinguish a network error from something
else.  I'm just in doubt about partial reads; those can return a positive error,
in which case you can return ESHUTDOWN (in read_sync).


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