On Thu 18-10-18 01:15:13, Amir Goldstein wrote: > On Wed, Oct 17, 2018 at 10:12 PM Miklos Szeredi <miklos@xxxxxxxxxx> wrote: > > > >> - STATX_ALL definition is unclear, can this change, or is it fixed? > > >> If it's the former, than that's a backward compatibility nightmare. > > >> If it's the latter, then what's the point? > > > > > > The value can change over time. It is intended to reflect the current > > > state of affairs at the time the userspace program and kernel are compiled. > > > The value sent from userspace lets the kernel know what fields are in > > > the userspace struct, so it doesn't try to set fields that aren't there. > > > > What's the point of a userspace program specifying STATX_ALL? Without > > a way to programmatically query the interface definition it's useless: > > there's no way to guess which mask bit corresponds to which field, and > > what that field represents. > > > > And there will be programs out there which specify STATX_ALL without > > considering that in the future it may become slower as it is now due > > to a recompile. > > > > So what's the point exactly? > > > > > The value in the kernel allows masking off new fields from userspace that > > > it doesn't understand. > > > > Okay, but that has nothing to do with the UAPI. Even as an internal > > flag we should be careful, as it might grow uses which can have > > similar issues as the userspace one above. > > > > FYI, I identified a similar anti-pattern in fanotify UAPI when I wanted to > add new flags and did not want to change the UAPI _ALL_ constants. > This is how we plan to solve it: > https://github.com/amir73il/linux/commit/8c2b1acadb88ee4505ccc8bfdc665863111fb4cc Yeah, after fanotify experience I find foo_ALL constants useless if not dangerous for userspace. Kernel internal constants like this are IMO useful. Honza -- Jan Kara <jack@xxxxxxxx> SUSE Labs, CR
