Am 09.05.2012 16:05, schrieb Paolo Bonzini: > Il 09/05/2012 15:40, Kevin Wolf ha scritto: >>>> +#ifndef SEEK_DATA >>>> +#define SEEK_DATA 3 >>>> +#endif >>>> +#ifndef SEEK_HOLE >>>> +#define SEEK_HOLE 4 >>>> +#endif >> How is that going to be portable? You assume that on non-Linux you'll >> get -EINVAL, but what does guarantee that 3 or 4 aren't already used for >> the standard SEEK_* constants or for a different non-standard extension? > > While SEEK_* is not guaranteed by POSIX to be 0/1/2, the values is so > old that there may still exist programs that hard-code the values > (similar to O_RDONLY/O_WRONLY/O_RDWR, though probably not any other O_* > constant). It would be quite unwise to define them to something else. > Even MS-DOS reused the values! > > AFAIK this is the only extension of lseek that's ever been added. It > was done on Solaris first and then in Linux and the BSDs. It used 3/4 > there too, see for example http://bugs.python.org/msg119551 (Solaris) > and http://mail-index.netbsd.org/tech-kern/2011/08/17/msg011231.html > (NetBSD).
Why not simply #ifdef the whole code out and fall back to the current "everything is allocated" behaviour when SEEK_DATA/HOLE aren't defined? Kevin
