Re: Upcoming: Notifications, FS notifications and fsinfo()

[Karel Zak]

On Mon, Mar 30, 2020 at 10:28:56PM +0200, Miklos Szeredi wrote:
> All this could be solved with a string key/value representation of the
> same data, with minimal performance loss on encoding/parsing.  The
> proposed fs interface[1] is one example of that, but I could also
> imagine a syscall based one too.

Yes, key/value is possible solution. The question is if we really 
need to add extra /sys-like filesystem to get key/value ;-) I can 
imagine key/value from FD based interface without open/read/close for
each attribute,

    fd = open("/mnt", O_PATH);
    fsinfo(fd, "propagation", buf, sizeof(buf));
    fsinfo(fd, "fstype", buf, sizeof(buf));
    close(fd);

why I need /mountfs/<id>/propagation and /mountfs/<id>/fstype to get
the same? It sounds like over-engineering without any extra bonus.

Anyway, if we have FD based interfaces like fsopen(), fsmount(),
open_tree() and move_mount() then it sounds strange that you cannot
use the FD to ask kernel for the mount node attributes and you need 
to open and read another /sys-like files. 

IMHO it would be nice that after open(/mnt, O_PATH) I can do whatever
with the mount point (umount, move, reconfigure, query, etc.). Please,
try to keep it simple and consistent ;-)

    Karel

-- 
 Karel Zak  <kzak@xxxxxxxxxx>
 http://karelzak.blogspot.com