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15 .Dd $Mdocdate: July 30 2021 $
20 .Nd Simple Distributed File System
23 is a protocol that implements a distributed file systems.
24 It provides primitives to manage
25 .Pq create, read, write and delete
26 sets of files remotely.
27 These files don't necessarily need to be actually stored on a disk,
28 they may be, for example, synthesise on demand from external sources.
30 A client transmits requests
32 to a server, which returns replies
35 The combined acts of transmitting a request of a particular type and
36 receiving a reply is called a transaction of that type.
38 Each message consists of a sequence of bytes mostly grouped in one,
39 two or four integer fields transmitted in little-endian order
40 .Pq least significant byte first .
41 Data items of larger or variable lengths are represented by a two-byte
42 field specifying the length followed by the actual data.
43 The only exception to this rule are QIDs, thirteen byte long
44 objects, that are sent as-is.
46 Text strings are represented with a two-byte count and the sequence of
47 UNICODE codepoints encoded in UTF-8.
48 Text strings in 9p are not NUL-terminated.
49 The NUL-terminator is illegal in all text strings and thus excluded
50 from paths, user names and so on.
52 Fields are hereafter denoted as
53 .Bd -literal -offset indent
57 to indicate that type is one byte long, tag two and fid four.
58 Strings are denoted as name[s] and are sent on the wire as
59 .Bd -literal -offset indent
60 length[2] string[length]
63 A qid, described later, is a 13-byte value that is sent on the wire as
64 .Bd -literal -offset indent
65 type[1] version[4] path[8]
68 Every message has a header with the following fields:
69 .Bd -literal -offset indent
73 where len indicates the overall length of the message, including
74 itself; type is one byte indicating the type of the message and the
75 tag is a number choosen by the client that indicate uniquely the
77 Then follows an optional body whose structure depends on the type of
80 The message types are as follows:
81 .Bl -tag -width versionxx
83 Negotiate the version and maximum message size.
85 len[4] Tversion tag[2] msize[4] version[s]
86 len[4] Rversion tag[2] msize[4] version[s]
91 request must be the first message sent, and the client cannot issue
92 further requests until it has received the Rversion reply.
99 .Pq the maximum size for packets
100 and the protocol version used, the server replies with a
102 smaller or equal to the one proposed by the client.
103 The version string must always begin with the two character
105 If the server don't understand the client required version, should
106 reply with a Rversion using the version string
108 and not use a Rerror.
110 Populate the namespace
112 len[4] Tattach tag[2] fid[4] afid[4] uname[s] aname[s]
113 len[4] Rattach tag[2] qid[13]
118 len[4] Tclunk tag[2] fid[4]
122 Return an error string
124 len[4] Rerror tag[2] ename[s]
127 The Rerror message is used to return an error string describing the
128 failure of a request.
130 indicates the failed request.
131 Note that there isn't a Terror, and it's not possible for a server to
136 Abort an ongoing operation.
138 len[4] Tflush tag[2] oldtag[2]
