hi, Here's another "would be nice to have this on the record" sort of thing that I haven't been able to find any other public statements about. FILESYSTEM_MAX_STACK_DEPTH is defined in a non-public header as 2. As far as I can tell, there's no way to query the limit out of a running kernel, and there's no indication if this value might ever be increased. Hopefully it won't be decreased. I'm trying to write a userspace binding layer for supporting passthrough fds in fuse and it's hard to validate user input for the stacking depth parameter. libfuse hardcodes some constant values (0, 1) that the user might choose, but in an adjacent comment makes references to the "current" kernel, suggesting that it might change at some point. It's also sort of difficult to determine if a value is valid by probing: choosing an invalid value simply disables passthrough fd support, which you won't find out about until you actually go and try to create a passthrough fd, at which point it fails with EPERM (but which can also happen for many other reasons). So, I guess: - will 2 ever change? - if not, can we get it in a public header? - if so, can we add some sort of API to get the current value? Thanks in advance! lis
