On Mon, Aug 26, 2024 at 10:37:12PM GMT, Darrick J. Wong wrote: > On Tue, Aug 27, 2024 at 10:32:38AM +0800, Hongbo Li wrote: > > > > > > On 2024/8/27 10:13, Darrick J. Wong wrote: > > > On Tue, Aug 27, 2024 at 01:41:08AM +0000, Hongbo Li wrote: > > > > Many mainstream file systems already support the GETVERSION ioctl, > > > > and their implementations are completely the same, essentially > > > > just obtain the value of i_generation. We think this ioctl can be > > > > implemented at the VFS layer, so the file systems do not need to > > > > implement it individually. > > > > > > What if a filesystem never touches i_generation? Is it ok to advertise > > > a generation number of zero when that's really meaningless? Or should > > > we gate the generic ioctl on (say) whether or not the fs implements file > > > handles and/or supports nfs? > > > > This ioctl mainly returns the i_generation, and whether it has meaning is up > > to the specific file system. Some tools will invoke IOC_GETVERSION, such as > > `lsattr -v`(but if it's lattr, it won't), but users may not necessarily > > actually use this value. > > That's not how that works. If the kernel starts exporting a datum, > people will start using it, and then the expectation that it will > *continue* to work becomes ingrained in the userspace ABI forever. > Be careful about establishing new behaviors for vfat. Is the meaning even the same across all filesystems? And what is the meaning of this anyway? Is this described/defined for userspace anywhere?
