posix_fallocate behavior in glibc

[Christoph Hellwig]

On Mon, Jul 29, 2024 at 09:23:22PM +0200, Florian Weimer wrote:
> Anything that's not EOPNOTSUPP will do.  EMEDIUMTYPE or ENOTBLK might do
> it.  Any of the many STREAMS error codes could also be re-used quite
> safely because Linux doesn't do STREAMS.

Huh?  EOPNOTSUP(P) is the standard error code in Posix for operation
not supported, and clearly documented as such in the Linux man page
(for musl).  A totally random new error code doesn't really help us.

> If you remove the fallback code, applications need to be taught about
> EOPNOTSUPP, so that doesn't really make a difference.

Portable software can't assume that posix_fallocate actually does
anything.