Re: [RFC 4/4] Add cat-blob report pipe from fast-import to remote-helper.

> On invocation of a helper a new pipe is opened.
> To close the other end after fork, the prexec_cb feature
> of the run_command api is used.
> If the helper is not used with fast-import later the pipe
> is unused.
> The FD is passed to the remote-helper via it's environment,
> helpers that don't use fast-import can simply ignore it.
> fast-import has an argv for that.
>
> Signed-off-by: Florian Achleitner <florian.achleitner.2.6.31@gmail.com>
> ---
>  transport-helper.c |   48 ++++++++++++++++++++++++++++++++++++++++++++++++
>  vcs-svn/svndump.c  |    9 ++++++++-
>  2 files changed, 56 insertions(+), 1 deletion(-)
>
> diff --git a/transport-helper.c b/transport-helper.c
> index 61c928f..b438040 100644
> --- a/transport-helper.c
> +++ b/transport-helper.c
> @@ -17,6 +17,7 @@ struct helper_data {
>        const char *name;
>        struct child_process *helper;
>        FILE *out;
> +       int fast_import_backchannel_pipe[2];
>        unsigned fetch : 1,
>                import : 1,
>                export : 1,
> @@ -98,19 +99,30 @@ static void do_take_over(struct transport *transport)
>        free(data);
>  }
>
> +static int fd_to_close;
> +void close_fd_prexec_cb(void)
> +{
> +       if(debug)
> +               fprintf(stderr, "close_fd_prexec_cb closing %d\n", fd_to_close);
> +       close(fd_to_close);
> +}
> +
>  static struct child_process *get_helper(struct transport *transport)
>  {
>        struct helper_data *data = transport->data;
>        struct strbuf buf = STRBUF_INIT;
> +       struct strbuf envbuf = STRBUF_INIT;
>        struct child_process *helper;
>        const char **refspecs = NULL;
>        int refspec_nr = 0;
>        int refspec_alloc = 0;
>        int duped;
>        int code;
> +       int err;
>        char git_dir_buf[sizeof(GIT_DIR_ENVIRONMENT) + PATH_MAX + 1];
>        const char *helper_env[] = {
>                git_dir_buf,
> +               NULL,   /* placeholder */
>                NULL
>        };
>
> @@ -133,6 +145,24 @@ static struct child_process *get_helper(struct transport *transport)
>        snprintf(git_dir_buf, sizeof(git_dir_buf), "%s=%s", GIT_DIR_ENVIRONMENT, get_git_dir());
>        helper->env = helper_env;
>
> +
> +       /* create an additional pipe from fast-import to the helper */
> +       err = pipe(data->fast_import_backchannel_pipe);
> +       if(err)
> +               die("cannot create fast_import_backchannel_pipe: %s", strerror(errno));
> +
> +       if(debug)
> +               fprintf(stderr, "Remote helper created fast_import_backchannel_pipe { %d, %d }\n",
> +                               data->fast_import_backchannel_pipe[0], data->fast_import_backchannel_pipe[1]);
> +
> +       strbuf_addf(&envbuf, "GIT_REPORT_FILENO=%d", data->fast_import_backchannel_pipe[0]);
> +       helper_env[1] = strbuf_detach(&envbuf, NULL);
> +
> +       /* after the fork, we need to close the write end in the helper */
> +       fd_to_close = data->fast_import_backchannel_pipe[1];
> +       /* the prexec callback is run just before exec */
> +       helper->preexec_cb = close_fd_prexec_cb;
> +
>        code = start_command(helper);
>        if (code < 0 && errno == ENOENT)
>                die("Unable to find remote helper for '%s'", data->name);
> @@ -141,6 +171,7 @@ static struct child_process *get_helper(struct transport *transport)
>
>        data->helper = helper;
>        data->no_disconnect_req = 0;
> +       free((void*)helper_env[1]);
>
>        /*
>         * Open the output as FILE* so strbuf_getline() can be used.
> @@ -237,6 +268,10 @@ static int disconnect_helper(struct transport *transport)
>                        xwrite(data->helper->in, "\n", 1);
>                        sigchain_pop(SIGPIPE);
>                }
> +               /* close the pipe, it is still open if it wasn't used for fast-import. */
> +               close(data->fast_import_backchannel_pipe[0]);
> +               close(data->fast_import_backchannel_pipe[1]);
> +
>                close(data->helper->in);
>                close(data->helper->out);
>                fclose(data->out);
> @@ -376,13 +411,20 @@ static int fetch_with_fetch(struct transport *transport,
>  static int get_importer(struct transport *transport, struct child_process *fastimport)
>  {
>        struct child_process *helper = get_helper(transport);
> +       struct helper_data *data = transport->data;
> +       struct strbuf buf = STRBUF_INIT;
>        memset(fastimport, 0, sizeof(*fastimport));
>        fastimport->in = helper->out;
>        fastimport->argv = xcalloc(5, sizeof(*fastimport->argv));
>        fastimport->argv[0] = "fast-import";
>        fastimport->argv[1] = "--quiet";
> +       strbuf_addf(&buf, "--cat-blob-fd=%d", data->fast_import_backchannel_pipe[1]);
> +       fastimport->argv[2] = strbuf_detach(&buf, NULL);
>
>        fastimport->git_cmd = 1;
> +
> +       fd_to_close = data->fast_import_backchannel_pipe[0];
> +       fastimport->preexec_cb = close_fd_prexec_cb;
>        return start_command(fastimport);
>  }
>
> @@ -427,6 +469,11 @@ static int fetch_with_import(struct transport *transport,
>        if (get_importer(transport, &fastimport))
>                die("Couldn't run fast-import");
>
> +
> +       /* in the parent process we close both pipe ends. */
> +       close(data->fast_import_backchannel_pipe[0]);
> +       close(data->fast_import_backchannel_pipe[1]);
> +
>        for (i = 0; i < nr_heads; i++) {
>                posn = to_fetch[i];
>                if (posn->status & REF_STATUS_UPTODATE)
> @@ -441,6 +488,7 @@ static int fetch_with_import(struct transport *transport,
>
>        if (finish_command(&fastimport))
>                die("Error while running fast-import");
> +       free((void*)fastimport.argv[2]);
>        free(fastimport.argv);
>        fastimport.argv = NULL;
>
> diff --git a/vcs-svn/svndump.c b/vcs-svn/svndump.c
> index 2f0089f..b1fe03f 100644
> --- a/vcs-svn/svndump.c
> +++ b/vcs-svn/svndump.c
> @@ -467,7 +467,14 @@ void svndump_read(const char *url)
>
>  static void init()
>  {
> -       fast_export_init(REPORT_FILENO);
> +       int report_fd;
> +       char* back_fd_env = getenv("GIT_REPORT_FILENO");
> +       if(!back_fd_env || sscanf(back_fd_env, "%d", &report_fd) != 1) {
> +               warning("Cannot get cat-blob fd from environment, using default!");
> +               report_fd = REPORT_FILENO;
> +       }
> +
> +       fast_export_init(report_fd);
>        strbuf_init(&dump_ctx.uuid, 4096);
>        strbuf_init(&dump_ctx.url, 4096);
>        strbuf_init(&rev_ctx.log, 4096);
> --
> 1.7.9.5