Reading named pipes on linux in OpenJDK gives me "OSError, [Errno 5] Illegal seek"

[HolgerHees]

I'm using graalpy 24.2.1 as a maven dependency for my Java Project running in OpenJDK.

If I try to read from a named pipe on linux like below

cd /tmp/
mkfifo myPipe
echo "My pipe content" > myPipe

and my python code looks like

file = open("/tmp/myPipe", "rb")
file.read(1)

running the above example with graalpy binary, it works. But if I run the same in OpenJDK, I get "OSError, [Errno 5] Illegal seek"

The context is created with

.allowHostAccess(HostAccess.ALL)
.allowAllAccess(true)
.hostClassLoader(getClass().getClassLoader())
.allowNativeAccess(true)
.allowExperimentalOptions(true)
.option("python.PosixModuleBackend", "java")

[timfel]

The calls that happen are these:

[python::LoggingPosixSupport] FINER: lseek(3, 0, 1)
[python::LoggingPosixSupport] FINER: lseek -> throw errno=5, msg='Illegal seek'
[python::LoggingPosixSupport] FINER: read(3, 8192)
[python::LoggingPosixSupport] FINER: read -> throw errno=5, msg='Illegal seek' 

The seek is a 0 bytes seek and 1 is SEEK_CUR. In lseek in EmulatedPosixSupport.java we raise when the underlying channel is not seekable, but for this specific case we can just accept and return since we don't actually need to change the position.