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export - export a name space


include "sys.m";
sys := load Sys Sys->PATH;

export:   fn(fd: ref FD, dir: string, flag: int):   int;


Export receives and replies to 9P requests from a client on a connection represented by fd, for file operations on the part of the current file name space rooted at dir, which is thus exported. This is the server end of the client's mount call. Names presented by the client are interpreted relative to directory dir, which can be adjusted using sys-pctl(2) and sys-bind(2) before export. The file descriptor fd must be open for reading and writing, and neither mounted elsewhere nor already exported.

Commonly, export's first argument is a file descriptor open on the data file in the dir of a Connection returned by listen (see dial(2)). Before calling export, the connection on fd can optionally be authenticated and set for encryption or digesting using the functions in security-auth(2).

The export function takes two mutually exclusive flags:

Export blocks until all client requests are complete.
Client requests are handled by a background (kernel) process. Export returns immediately. The serving process terminates when the client hangs up.


Export a given directory on fd, protecting it from subsequent changes:

exportdir(fd: ref Sys->FD, dir: string, pid: chan of int)
	pid <-= sys->pctl(Sys->FORKNS|Sys->FORKENV|Sys->NEWFD, fd.fd :: nil);
	sys->export(fd, dir, Sys->EXPWAIT);

The FORKNS given to pctl forks the name space, and prevents the sys->export from seeing the effects of subsequent mounts by the process that calls or spawns exportdir. The exportdir function above might be called using:

pid := chan of int;
spawn exportdir(fd, "/", pid);
expid := <-pid;

Service will stop automatically when the connection fd returns end-of-file (eg, when it hangs up), but it can also be stopped locally by killing expid.




Export returns a non-negative value on success and -1 on error; the system error string is set.

SYS-EXPORT(2 ) Rev:  Tue Mar 31 02:42:39 GMT 2015