[9fans] wstat and atomic directory change

[Giacomo Tesio <giacomo@tesio.it>]

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Hi, I'm wondering about the validity of an interpretation of intro(5) and
stat(5) that could allow a server to atomically change the directory of a
file.

>From intro(5) <http://man.cat-v.org/9front/5/intro>

The notation
string[s] (using a literal s character) is shorthand for
s[2] followed by s bytes of UTF-8 text.  (Systems may choose
to reduce the set of legal characters to reduce syntactic
problems, for example to remove slashes from name compo-
nents, *but the protocol has no such restriction*.  Plan 9
names may contain any printable character (that is, any
character outside hexadecimal 00-1F and 80-9F) except
slash.).


 wstat(5) <http://man.cat-v.org/9front/5/stat> on the other hand does not
say much about the name field of Fcall:

The name can be changed by anyone with write
permission in the parent directory; it is an error to change
the name to that of an existing file.

Now, since the protocol does not restrict names (even if Plan 9 does it),
I'm wondering if setting the name to a full path starting from root could
be used to change atomically the directory of a file (given the write
permission on both original and target directory).

Obviously I'm not referring to Plan 9 file servers (I guess this would be a
non retrocompatbile change), but I'm considering if such interpretation
would be wrong (according to the official specifications).

A server supporting such behaviour could be considered a 9p2000 conformant
server?


Giacomo

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