run-command: add pre-exec callback

This is a function provided by the caller which is called
_after_ the process is forked, but before the spawned
program is executed. On platforms (like mingw) where
subprocesses are forked and executed in a single call, the
preexec callback is simply ignored.

This will be used in the following patch to do some setup
for 'less' that must happen in the forked child.

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

diff --git a/run-command.c b/run-command.c
index 6e29fdf9e2968900d21ea48b992f292204621f19..73d0c312767191a2150b5223806c1733533bc5c2 100644 (file)
--- a/run-command.c
+++ b/run-command.c
@@ -110,6 +110,8 @@ int start_command(struct child_process *cmd)
                                        unsetenv(*cmd->env);
                        }
                }
+               if (cmd->preexec_cb)
+                       cmd->preexec_cb();
                if (cmd->git_cmd) {
                        execv_git_cmd(cmd->argv);
                } else {

diff --git a/run-command.h b/run-command.h
index 5203a9ebb10b14bd06862abafed0ab73d7514a3d..4f2b7d7d403ee6d87fea5ba2dc32da7596965e5e 100644 (file)
--- a/run-command.h
+++ b/run-command.h
@@ -42,6 +42,7 @@ struct child_process {
        unsigned no_stderr:1;
        unsigned git_cmd:1; /* if this is to be git sub-command */
        unsigned stdout_to_stderr:1;
+       void (*preexec_cb)(void);
 };
 
 int start_command(struct child_process *);