EINVAL, that error code is ignored, leaving whatever other meaningful
error code that might have previously been returned intact. Stand-alone
file system implementations return EINVAL typically when the file system
is not recognized (i.e. cd9660_open on a UFS file system, ufs_open on a
cd9660 file system, etc.). This meant that if you had multiple file
systems in a file system switch, the first returned ENOENT (because
it recognized the file system type, but the file wasn't there) and
the second returned EINVAL (because it didn't recognize the file system
type), errno would be set to EINVAL. Now it'll be set to ENOENT.
It would probably make sense to have file systems return a special
error code to indicate "this file system is unrecognized," which
could then be special-cased, but that's a fair bit more invasive.
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