On Wed, Aug 28, 2024 at 12:48 PM Amir Goldstein <amir73il@xxxxxxxxx> wrote:
> > Similarly, it looks like the first backing ID is usually 1. Is it
> > guaranteed that 0 is never a valid backing ID? I am not sure, and it
> > would certainly help implementation on my side.
>
> No guarantee.
> There was some suggestion about special use for value 0,
> but I don't remember what it was right now.
In a file system, not all inodes are backed by a file. If 0 would not
be handed out as an ID, then backing ID=0 could mean: this node is not
backed by a file (and doesn't need to unregister the ID on
forget/release). If 0 is a valid ID, I either have to add another
boolean to the inode, or keep calling the ioctl until I get a non-zero
value.
Reading, the code, the call is
id = idr_alloc_cyclic(&fc->backing_files_map, fb, 1, 0, GFP_ATOMIC);
ie. start=1. In other words, if the counter wraps, it will start at 1
again, and 0 is not handed out.
--
Han-Wen Nienhuys - hanwenn@xxxxxxxxx - http://www.xs4all.nl/~hanwen
