ATTACH(5) ATTACH(5)
NAME
attach, auth - messages to establish a connection
SYNOPSIS
size[4] Tauth tag[2] afid[4] uname[s] aname[s]
size[4] Rauth tag[2] aqid[13]
size[4] Tattach tag[2] fid[4] afid[4] uname[s] aname[s]
size[4] Rattach tag[2] qid[13]
DESCRIPTION
The attach message serves as a fresh introduction from a
user on the client machine to the server. The message iden-
tifies the user (uname) and may select the file tree to
access (aname). The afid argument specifies a fid previ-
ously established by an auth message, as described below.
As a result of the attach transaction, the client will have
a connection to the root directory of the desired file tree,
represented by fid. An error is returned if fid is already
in use. The server's idea of the root of the file tree is
represented by the returned qid.
If the client does not wish to authenticate the connection,
or knows that authentication is not required, the afid field
in the attach message should be set to NOFID, defined as
(u32int)~0 in <fcall.h>. If the client does wish to authen-
ticate, it must acquire and validate an afid using an auth
message before doing the attach.
The auth message contains afid, a new fid to be established
for authentication, and the uname and aname that will be
those of the following attach message. If the server does
not require authentication, it returns Rerror to the Tauth
message.
If the server does require authentication, it returns aqid
defining a file of type QTAUTH (see intro(5)) that may be
read and written (using read and write messages in the usual
way) to execute an authentication protocol. That protocol's
definition is not part of 9P itself.
Once the protocol is complete, the same afid is presented in
the attach message for the user, granting entry. The same
validated afid may be used for multiple attach messages with
the same uname and aname.
ENTRY POINTS
An attach transaction will be generated for kernel devices
(see intro(3)) when a system call evaluates a file name
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ATTACH(5) ATTACH(5)
beginning with `#'. Pipe(2) generates an attach on the ker-
nel device pipe(3). The mount system call (see bind(2)) gen-
erates an attach message to the remote file server. When
the kernel boots, an attach is made to the root device,
root(3), and then an attach is made to the requested file
server machine.
An auth transaction is generated by the fauth(2) system call
or by the first mount system call on an uninitialized con-
nection.
SEE ALSO
auth(2), fauth(2), version(5), authsrv(6)
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