On 29 January 2015 at 09:04, Giacomo Tesio <giacomo@tesio.it> wrote:

> What's the meaning of qids? I see that responses often include them but
> request messages do not.
>
    see intro(5) or intro(9P) depending on system. They identify a file on
a server; they are a value provided by the server to the client,
    so they only appear in replies.

> What's the proper message sequence to delete a file? And to delete a non
> empty directly?
>
    You point a fid at the file, then remove it:    Twalk* ... Tremove
    A non-empty directory can't be removed.
    Tremove implies Tclunk

>  Is it possible to move a file between different directories atomically?
>
    No.

> I can't find details on the file execution permission: looks like a
> malicious client could just ignore it on files and execute anything that it
> can read (obviously I'm just talking about single files,  not directory).
>
    It's not malicious, just incorrect. Obviously you can't execute a
remote image or script unless you read it.
    The existing servers treat OEXEC as opening for read, with a check of
the X permission.
    A directory, however, can't be opened OEXEC.
    In the script case, the file server will allow the OEXEC open, but
#!interpreter is converted to {interpreter file},
    and then if the file is x-only, the subsequent open for OREAD will
fail. Possibly the interpreters should open OEXEC, but they don't.

> When I should clunk the afid?
>
    When the client closes it.

> What about encryption? Is it completely delegated to the transport layer?
>
     Yes, for encryption of communication.  A file server could encrypt
files or the whole storage structure.