fcat can't print anything in my system

[federicotorrielli]

Hi, maybe it's some dependency that dependabot broke but my fcat is not working anymore, it gives me this error:

Thanks in advance for the support!

[mre]

Strange. That means it has problems reading from the kernel buffer or printing to the screen.
Can you try a few different files?
What is your kernel version and linux distribution?

[federicotorrielli]

I'm using ArcoLinux with 5.9.11-arch2-1 kernel, it gives the error on every file, even in the /home folder.

[federicotorrielli]

Any update on this?

[mre]

Unfortunately not from my side. Don't know how to debug this as I don't have any system to debug the issue. 😟 Can you try on a different distribution if you have any at hand?

[federicotorrielli]

All right! So, I did some test on a lot of distros in these days. Here's my report:

On every distribution with linux 5.9.* and 5.10.* fcat does not work BUT on every linux 5.8 and 5.4 does work without any problem.
So I guess the problem is really something that has to be related to the latest linux versions.
Tell me if you need more testing, I'll be glad to do so.

[mre]

This is utterly confusing... and a bit scary. So it sounds like something changed/broke in 5.9 (most likely changed).

[mre]

Why was that closed? I'd still say it would be interesting to know the reason why it is not working. Perhaps someone wants to pick this up in the future?

[federicotorrielli]

Well, my bad. I close issues that are more than 2 months old, because it always means that a project is currently inactive. And also the issue seems related to the new kernels so people stick with bat (which is also using the splice feature) because it's currently active and has newer features.
Can you re-open the issue? I'm currently on mobile and there's no choice to open it again here. Thanks!

[mre]

bat uses splice? That's news to me. I couldn't find any hint in the source code, only two issues, one closed and the other open but stalled.

• Use of Linux splice command in plain-text mode for performance increase sharkdp/bat#1112
• Use splice? sharkdp/bat#194

Anything I'm missing here?

[kangalio]

It seems like stdout doesn't count as a pipe anymore for some reason

fcat file.txt | cat works, fcat file.txt does not. This seems to be a common issue, e.g. someone on StackOverflow using splice from C. It was mentioned that this issue starts with Linux 5.9, so maybe this is related?

[mre]

I looked through the 5.9 changelog and could only find this patch, which describes a deadlock in combination with splice. Can't find much else. Maybe somebody with more kernel experience can verify.

[kangalio]

Oops, I meant to add this link to my last sentence http://archive.lwn.net:8080/linux-kernel/202105071116.638258236E@keescook/t/

[mre]

So does that mean we have to ask on the Linux Kernel mailing list if they can add back support for splice for our use-case? 😅