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COMPAT_30(8) System Manager's Manual COMPAT_30(8)

compat_30 — setup procedure for backward compatibility on post-3.0 releases

options COMPAT_30

The compat_30 module allows NetBSD to run NetBSD 3.0 executables.

The support is present if the kernel was built with option COMPAT_30. It is not available as a loadable module.

Static executables typically need no additional setup. Dynamic binaries may require shared libraries whose major version number changed since NetBSD 3.0, which are listed below. A shadow directory under /emul is not used; the libraries can be obtained from a NetBSD 3.0 distribution and installed in the original directories shown, as the major version number in the file name will prevent conflicts. If an upgrade installation from NetBSD 3.0 has been done and these libraries are still present, nothing more need be done.

COMPAT_30 enables the NetBSD 3.0 versions of the following system calls, whose syscall numbers and argument structures were changed after the 3.0 release to accommodate 64-bit filesystems: fhstat(2), fstat(2), getdents(2), lstat(2), stat(2).

The filehandle structure (formerly fhandle_t) was made opaque to userland and variable-sized. A fh_size argument was added to related syscalls: fhstat(2), fhstatvfs(2), fhstatvfs1(2), fhopen(2), getfh(2). This changes the API and ABI of those syscalls, COMPAT_30 enables binary compatibility with the old ABI. Source compatibility is not provided, as use of those syscalls is supposed to be rare.

The error code from the socket(2) syscall changed from EPROTONOSUPPORT to EAFNOSUPPORT in the case of an unsupported address family. COMPAT_30 enables binary compatibility with the old ABI. Source compatiblility is not provided.

The struct ntptimeval used by ntp_gettime(2) changed with the implementation of timecounters.

config(1), fhstat(2), fstat(2), getdents(2), lstat(2), stat(2), options(4)

NetBSD offers back-compatibility options back to NetBSD 0.9, but the first to be documented with a manual page is compat_30.

The compatible getdents(2) is unable to see directory entries beneath the top layer of a union, even though the real 3.0 getdents() did not have that problem.

Programs with security impact that receive incorrect directory contents from getdents() may behave improperly, as when they are unable to find, or find the wrong versions of, important files.

December 15, 2007 NetBSD-9.2