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-rw-r--r--Documentation/git-fast-import.txt42
1 files changed, 39 insertions, 3 deletions
diff --git a/Documentation/git-fast-import.txt b/Documentation/git-fast-import.txt
index 45101ca957..2620d28b4b 100644
--- a/Documentation/git-fast-import.txt
+++ b/Documentation/git-fast-import.txt
@@ -98,9 +98,10 @@ OPTIONS
options.
--cat-blob-fd=<fd>::
- Specify the file descriptor that will be written to
- when the `cat-blob` command is encountered in the stream.
- The default behaviour is to write to `stdout`.
+ Write responses to `cat-blob` and `ls` queries to the
+ file descriptor <fd> instead of `stdout`. Allows `progress`
+ output intended for the end-user to be separated from other
+ output.
--done::
Require a `done` command at the end of the stream.
@@ -942,6 +943,9 @@ This command can be used anywhere in the stream that comments are
accepted. In particular, the `cat-blob` command can be used in the
middle of a commit but not in the middle of a `data` command.
+See ``Responses To Commands'' below for details about how to read
+this output safely.
+
`ls`
~~~~
Prints information about the object at a path to a file descriptor
@@ -991,6 +995,9 @@ instead report
missing SP <path> LF
====
+See ``Responses To Commands'' below for details about how to read
+this output safely.
+
`feature`
~~~~~~~~~
Require that fast-import supports the specified feature, or abort if
@@ -1079,6 +1086,35 @@ If the `--done` command line option or `feature done` command is
in use, the `done` command is mandatory and marks the end of the
stream.
+Responses To Commands
+---------------------
+New objects written by fast-import are not available immediately.
+Most fast-import commands have no visible effect until the next
+checkpoint (or completion). The frontend can send commands to
+fill fast-import's input pipe without worrying about how quickly
+they will take effect, which improves performance by simplifying
+scheduling.
+
+For some frontends, though, it is useful to be able to read back
+data from the current repository as it is being updated (for
+example when the source material describes objects in terms of
+patches to be applied to previously imported objects). This can
+be accomplished by connecting the frontend and fast-import via
+bidirectional pipes:
+
+====
+ mkfifo fast-import-output
+ frontend <fast-import-output |
+ git fast-import >fast-import-output
+====
+
+A frontend set up this way can use `progress`, `ls`, and `cat-blob`
+commands to read information from the import in progress.
+
+To avoid deadlock, such frontends must completely consume any
+pending output from `progress`, `ls`, and `cat-blob` before
+performing writes to fast-import that might block.
+
Crash Reports
-------------
If fast-import is supplied invalid input it will terminate with a