tail: unnecessary pipe2 syscall for empty files

[dragutreis]

Description:
When running tail -c +1 /dev/null, tail makes an unnecessary pipe2
syscall even though the file is empty and has no data to transfer.
The pipe creation is wasteful in this case.

Steps to reproduce:

strace -c -e pipe,pipe2 tail -c +1 /dev/null

Expected behavior: No pipe2 syscall for empty/exhausted files.

Actual behavior: 1 pipe2 call despite nothing to transfer.

[oech3]

Note that this is resource issue instead of compatibility issue (GNU does not call it is not an issue).
pipe itself is needed for zero-copy.

[oech3]

This is not a high-priority, but I might add threshould for usage of splice. strace says GNU cat does not use splice for file < 64KiB.

[dragutreis]

Alright, good to know.