On 12/16/2017 08:49 AM, Avi Kivity wrote: > > > On 12/14/2017 09:15 PM, Goldwyn Rodrigues wrote: >> >> 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 > > Which of these are returned from io_submit() and which are returned in > the iocb? These are returned in iocb. > >> 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. > > So the application must know about filesystem mount points, and be > prepared to create a file and try to write it (in case the filesystem is > empty) or alter its behavior during runtime depending on the errors it > sees. Well yes. Hopefully, the application knows what it is doing when it performs RWF_NOWAIT. -- 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
