select() does not support a first argument up to FD_SETSIZE

[bhaible]

The function select(), specified in ​https://pubs.opengroup.org/onlinepubs/9799919799/functions/select.html , should support a first argument up to FD_SETSIZE. This is clear

• from the definition of FD_SETSIZE as the number of bits in an fd_set,
• because if "The nfds argument is less than 0 or greater than FD_SETSIZE." an error EINVAL must be produced.

In Haiku (as of 2024-07-15), a first argument > FD_SETSIZE/2, <= FD_SETSIZE produces an error EINVAL. It shouldn't.

How to reproduce:

$ gcc foo.c
$ ./a.out
FD_SETSIZE = 1024
select: Invalid Argument

[bhaible]

test case foo.c

[waddlesplash]

The kernel returns EINVAL here because it knows the process doesn't have at least 513 opened FDs.

[bhaible]

The kernel returns EINVAL here because it knows the process doesn't have at least 513 opened FDs.

This is not a valid reason to fail with EINVAL:

• Quote: "The nfds argument specifies the range of descriptors to be tested. The first nfds descriptors shall be checked in each set; that is, the descriptors from zero through nfds-1 in the descriptor sets shall be examined." Since all three fd_set arguments are NULL, none of the file descriptors in the range 0..nfds-1 needs to be examined.

• If one of the file descriptor sets would contain an FD that is invalid or not open, the correct error code for that case would be EBADF.

[bhaible]

Many packages call select() with a first argument of FD_SETSIZE: algol68g, GNU bash, bogl, GNU clisp, flrig, GNU gcc, GNU gdb, GNU gnupg, graphviz, imview, librep, GNU octave, pmacct, GNU poke, GNU readline, simgear, singular, sympathy, GNU texinfo, etc.

See ​https://codesearch.debian.net/search?q=select+%28FD_SETSIZE%2C&literal=1&perpkg=1