Segfault when opening unseekable file on Cygwin

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Segfault when opening unseekable file on Cygwin #4804

Open mattjala opened 2 months ago

mattjala commented 2 months ago

Describe the bug test_unseekable_file() results in a segfault when run on Cygwin.

Expected behavior Opening an unseekable file should fail, or at least not segfault.

Platform (please complete the following information)

HDF5 develop as of 4ffeb77
Cygwin version 2.932
gcc 12.4.0-3
Ninja 1.12.0-1
Build shared libs disabled, since these have issues with Cygwin
parallel/mpi disabled

Additional context See #4797 for discussion

mattjala commented 2 months ago

This is a result of pwrite returning -1 when trying to write to /dev/null on Cygwin, but not on Linux. Note that despite what the name of the test implies, lseek does not return an error when accesing /dev/null on either Cygwin or Linux - so it should probably be renamed.

The failed assertion can be replicated on Linux by replacing the call to pwrite in H5FD__sec2_write() with a fake failure. I'm still looking into how this results in the specific error within the metadata cache.