'Error: No space left on device (os error 28)' when watching too many files

[jyn514]

System details

• OS/Platform name and version: Linux build-server 4.19.0-10-amd64 #1 SMP Debian 4.19.132-1 (2020-07-24) x86_64 GNU/Linux
• Rust version (if building from source): rustc --version: rustc 1.49.0-nightly (ffe52882e 2020-10-30)
• Notify version (or commit hash if building from git): 5.0.0-pre.3

• If you're coming from a project that makes use of Notify, what it is, and a link to the downstream issue if there is one: See bacon crashes on rustc Canop/bacon#10.
• Filesystem type and options: ext4, errors=remount-ro
• If you're running as a privileged user (root, System): no

What you did (as detailed as you can)

I ran notify on src/ of rust-lang/rust with RecursiveMode::Recursive.

What you expected

Either it should work, or notify should give a helpful error when trying to watch too many files.

What happened

notify printed Error: No space left on device (os error 28).

[0xpr03]

Quick note: You may already know about raising your max-files limit to watch. The error reported is not correct, I'll have to see whether this is labeled wrongly or may be coming from an internal (std?) part that reports this code as "no space left".

[jyn514]

$ man inotify_add_watch
       ENOSPC The  user  limit on the total number of inotify watches was reached or the kernel failed to allocate a needed
              resource.

Looks like this is wrong in the standard library - ENOSPC should not always be described as 'no space left'.

[0xpr03]

(Appeared also in #103 )

[jyn514]

@0xpr03 an option to workaround the upstream issue is to wrap io::Error in a new error type if the error is ENOSPC. Then you could give a more helpful error message.

[jyn514]

It turns out this is a bug in libc itself 🤦 rust-lang/rust#78723 (comment). So I think it makes sense to fix in notify, even though it shouldn't have to.

[0xpr03]

Yeah, I'll do a change for this.

[0xpr03]

This is released for v4 in 4.0.16

[0xpr03]

And for v5 in 5.0.0-pre.7