On 12/14/2017 11:38 AM, Avi Kivity wrote: > I'm looking to add support for RWF_NOWAIT within a linux-aio iocb. > Naturally, I need to detect at runtime whether the kernel support > RWF_NOWAIT or not. > > > The only method I could find was to issue an I/O with RWF_NOWAIT set, > and look for errors. This is somewhat less than perfect: > > - from the error, I can't tell whether RWF_NOWAIT was the problem, or > something else. If I enable a number of new features, I have to run > through all combinations to figure out which ones are supported and > which are not. Here is the return codes for RWF_NOWAIT EINVAL - not supported (older kernel) EOPNOTSUPP - not supported EAGAIN - supported but could not complete because I/O will be delayed 0 - supported and I/O completed (success). > > - RWF_NOWAIT support is per-filesystem, so I can't just remember not to > enable RWF_NOWAIT globally, I have to track it per file. Yes, the support is per filesystem. So, the application must know if the filesystem supports it, possibly by performing a small I/O. -- Goldwyn -- To unsubscribe from this list: send the line "unsubscribe linux-xfs" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
