[Libguestfs] [PATCH 1/2] Define .errno_is_preserved constant instead of a .errno_is_reliable callback.

[Richard W.M. Jones]

On Mon, Feb 06, 2017 at 11:00:48AM -0600, Eric Blake wrote:
> On 02/06/2017 08:57 AM, Richard W.M. Jones wrote:
> > The callback doesn't make much sense: Could the value change
> > per-connection?  Unlikely.  This is a property of the plugin as a
> > whole.
> > 
> > I changed the name to "errno_is_preserved", because it's not about the
> > reliability of errno, but about whether errno is preserved across
> > calls.
> 
> Makes it possible for a regression in C plugins (previously, such
> plugins implicitly behaved as if .errno_is_preserved was 1, now such
> plugins default to .errno_is_preserved == 0 unless explicitly set and
> recompiled against newer headers).  Thus, such plugins will now fail
> with EIO where they used to fail with reasonable errno values.
> 
> But I guess we can live with that.

Good point.  However I think another point is that setting
.errno_is_preserved requires some code inspection of all the
error paths, and I don't think that existing binary drivers
would necessarily get that right.

Thanks for looking at this.

Rich.

-- 
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