From: Jonathan Nieder <jrnieder@gmail.com>
To: Florian Achleitner <florian.achleitner.2.6.31@gmail.com>
Cc: Steven Michalske <smichalske@gmail.com>,
git@vger.kernel.org, David Michael Barr <davidbarr@google.com>,
Sverre Rabbelier <srabbelier@gmail.com>,
Jeff King <peff@peff.net>, Johannes Sixt <j.sixt@viscovery.net>,
Ramkumar Ramachandra <artagnon@gmail.com>
Subject: Re: [RFC 1/4 v2] Implement a basic remote helper for svn in C.
Date: Sat, 28 Jul 2012 01:54:39 -0500 [thread overview]
Message-ID: <20120728065439.GB4739@burratino> (raw)
In-Reply-To: <9398008.kKbpiTCtsb@flomedio>
Hi,
Some quick details.
Florian Achleitner wrote:
> Anyways, specifying cat-blob-fd is not
> allowed via the 'option' command (see Documentation and 85c62395).
> It wouldn't make too much sense, because the file descriptor must be set up by
> the parent.
>
> But for the fifo, it would, probably.
More precisely, requiring that the cat-blob fd go on the command line
instead of in the stream matches a model where fast-import's three
standard streams are abstract:
- its input, using the INPUT FORMAT described in git-fast-import(1)
- its standard output, which echoes "progress" commands
- its backflow stream, where responses to "cat-blob" and "ls" commands go
The stream format is not necessarily pinned to a Unix model where
input and output are based on filesystems and file descriptors. We
can imagine a fast-import backend that runs on a remote server and the
transport used for these streams is sockets; for fast-import frontends
to be usable in such a context, the streams they produce must not rely
on particular fd numbers, nor on pathnames (except for mark state
saved to relative paths with --relative-marks) representing anything
in particular.
This goes just as much for a fifo set up on the filesystem where the
fast-import backend runs as for an inherited file descriptor. In the
current model, such backend-specific details of setup go on the
command line.
> The backward channel is only used by the
> commands 'cat-blob' and 'ls' of fast-import. If a remote helper wants to use
> them, it would could make fast-import open the pipe by sending an 'option'
> command with the fifo filename, otherwise it defaults to stdout (like now) and
> is rather useless.
I'm getting confused by terminology again. Let's see if I have the cast
of characters straight:
- the fast-import backend (e.g., "git fast-import" or "hg-fastimport")
- the fast-import frontend (e.g., "git fast-export" or svn-fe)
- git's generic foreign VCS support plumbing, also known as
transport-helper.c
- the remote helper (e.g., "git remote-svn" or "git remote-testgit")
Why would the fast-import backend ever need to open a pipe? If I want
it to write backflow to a fifo, I can use
mkfifo my-favorite-fifo
git fast-import --cat-blob-fd=3 3>my-favorite-fifo
If I want it to write backflow to a pipe, I can use (using ksh syntax)
cat |&
git fast-import --cat-blob-fd=3 3>&p
> This would take the fifo setup out of transport-helper. The remote-helper would
> have to create it, if it needs it.
We can imagine transport-helper.c learning the name of a fifo set up by
the remote helper by sending it the "capabilities" command:
git> capabilities
helper> option
helper> import
helper> cat-blob-file my-favorite-fifo
helper> refspec refs/heads/*:refs/helper/remotename/*
helper>
transport-helper.c could then use that information to invoke
fast-import appropriately:
git fast-import --cat-blob-fd=3 3>my-favorite-fifo
But this seems like pushing complication onto the remote helper; since
there is expected to be one remote helper per foreign VCS,
implementing the appropriate logic correctly once and for all in
transport-helper.c for all interested remote helpers to take advantage
of seems to me like a better policy.
> Apropos stdout. That leads to another idea. You already suggested that it
> would be easiest to only use FDs 0..2. Currently stdout and stderr of fast-
> import go to the shell. We could connect stdout to the remote-helper and don't
> need the additional channel at all.
The complication that makes this strategy not so easy is "progress"
commands in the fast-import input stream. (Incidentally, it would be
nice to teach transport-helper.c to display specially formatted
"progress" commands using a progress bar some day.)
Hoping that clarifies,
Jonathan
next prev parent reply other threads:[~2012-07-28 6:54 UTC|newest]
Thread overview: 57+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-06-04 17:20 [RFC 0/4] Florian Achleitner
2012-06-04 17:20 ` [RFC 1/4] Implement a basic remote helper vor svn in C Florian Achleitner
2012-06-04 17:20 ` [RFC 2/4] Integrate remote-svn into svn-fe/Makefile Florian Achleitner
2012-06-04 17:20 ` [RFC 3/4] Add svndump_init_fd to allow reading dumps from arbitrary FDs Florian Achleitner
2012-06-04 17:20 ` [RFC 4/4] Add cat-blob report pipe from fast-import to remote-helper Florian Achleitner
2012-06-05 1:33 ` David Michael Barr
2012-06-05 6:56 ` Jeff King
2012-06-05 7:07 ` David Michael Barr
2012-06-05 8:14 ` Jeff King
2012-06-05 22:16 ` Florian Achleitner
2012-06-06 13:43 ` Jeff King
2012-06-06 21:04 ` Florian Achleitner
2012-06-05 8:51 ` Johannes Sixt
2012-06-05 9:07 ` Jeff King
2012-06-05 22:17 ` Florian Achleitner
2012-06-05 9:09 ` Johannes Sixt
2012-06-05 1:21 ` [RFC 3/4] Add svndump_init_fd to allow reading dumps from arbitrary FDs David Michael Barr
2012-06-29 7:49 ` [RFC 0/4 v2] Florian Achleitner
2012-06-29 7:54 ` [RFC 1/4 v2] Implement a basic remote helper for svn in C Florian Achleitner
2012-07-02 11:07 ` Jonathan Nieder
2012-07-06 0:30 ` Jonathan Nieder
2012-07-06 10:39 ` Florian Achleitner
2012-07-26 8:31 ` Florian Achleitner
2012-07-26 9:08 ` Jonathan Nieder
2012-07-26 16:16 ` Florian Achleitner
2012-07-28 7:00 ` Jonathan Nieder
2012-07-30 8:12 ` Florian Achleitner
2012-07-30 8:29 ` Jonathan Nieder
2012-07-30 13:55 ` Florian Achleitner
2012-07-30 16:55 ` Jonathan Nieder
2012-07-31 19:31 ` Florian Achleitner
2012-07-31 22:43 ` Jonathan Nieder
2012-08-01 8:25 ` Florian Achleitner
2012-08-01 19:42 ` Jonathan Nieder
2012-08-12 10:06 ` Florian Achleitner
2012-08-12 16:12 ` Jonathan Nieder
2012-08-12 19:39 ` Florian Achleitner
2012-08-12 20:10 ` Jonathan Nieder
2012-08-12 19:36 ` Jonathan Nieder
2012-07-26 17:29 ` Junio C Hamano
2012-07-30 8:12 ` Florian Achleitner
2012-07-26 9:45 ` Steven Michalske
[not found] ` <358E6F1E-8BAD-4F82-B270-0233AB86EF66@gmail.com>
2012-07-26 11:40 ` Jonathan Nieder
2012-07-26 14:28 ` Florian Achleitner
2012-07-26 14:54 ` Jonathan Nieder
2012-07-27 7:23 ` Florian Achleitner
2012-07-28 6:54 ` Jonathan Nieder [this message]
2012-06-29 7:58 ` [RFC 2/4 v2] Integrate remote-svn into svn-fe/Makefile Florian Achleitner
2012-06-29 7:59 ` [RFC 3/4 v2] Add svndump_init_fd to allow reading dumps from arbitrary FDs Florian Achleitner
2012-06-29 8:00 ` [RFC 4/4 v2] Add cat-blob report fifo from fast-import to remote-helper Florian Achleitner
2012-07-21 12:45 ` [RFC 4/4 v3] " Florian Achleitner
2012-07-21 14:48 ` Jonathan Nieder
2012-07-21 15:24 ` Florian Achleitner
2012-07-21 15:44 ` Jonathan Nieder
2012-07-22 21:03 ` Florian Achleitner
2012-07-22 21:24 ` Jonathan Nieder
2012-07-21 15:58 ` Jonathan Nieder
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