Created attachment 146391 [details] generic open program One might want to open files generically. However, one cannot open a UNIX socket file found in the filesystem. That fails with ENXIO. To workaround this one can use stat to check if the file is a socket first but that is racy. O_PATH offers a possible solution. As in the program below, one can open a file with O_PATH, check the file type with fstat and then open (and in the case of a socket bind or connect to) the file through the file descriptor. Unfortunately, while this works with connect, and open it fails with bind with EADDRINUSE.
This is not possible given the UNIX domain socket API is permanently fixed by Posix standards.
The only O_* constants defined by POSIX 2013 are: O_CLOEXEC, O_CREAT, O_DIRECTORY, O_EXCL, O_NOCTTY, O_NOFOLLOW, O_TRUNC, O_TTY_INIT, O_APPEND, O_DSYNC, O_NONBLOCK, O_RSYNC, O_SYNC, O_ACCMODE, O_EXEC, O_RDONLY, O_RDWR, O_SEARCH and O_WRONLY. Stephen Hemminger, behaviour relating to O_PATH has absolutely zero to do with UNIX sockets. If you have some other meaning you are unintelligible.
s/with UNIX sockets/with POSIX/g
> If the address family of the socket is AF_UNIX and the pathname in > address names a symbolic link, bind() shall fail and set errno to > [EADDRINUSE]. - POSIX 2013 Ah, I see what you mean now. That's really silly but I'll try to think and see if there's an alternate way of getting what I want.