# HG changeset patch
# User Paul Boddie <paul@boddie.org.uk>
# Date 1715360438 -7200
# Node ID 5c24477f91bf754ef0397f5b4554db6faf9f981b
# Parent  bbb065eae48318fbae56af1ca5754ac73499918f
Added the retention of the current data position in pipe endpoints, allowing
endpoints to be transferred to other programs and initialised appropriately.
Renamed the populated_size parameter in the flush operation to indicate that a
more general position is being sent, this being a populated size in a writing
context and the current reading position in a reading context.

diff -r bbb065eae483 -r 5c24477f91bf docs/wiki/Components
--- a/docs/wiki/Components	Fri May 10 14:49:52 2024 +0200
+++ b/docs/wiki/Components	Fri May 10 19:00:38 2024 +0200
@@ -404,11 +404,13 @@
 operation:
 
 {{{
-current_region(out offset_t populated_size, out offset_t size)
+current_region(inout offset_t position, out offset_t populated_size, out offset_t size)
 }}}
 
-This provides details of the populated size (or amount of written data) in a
-region along with the size of the region.
+This provides details of the recorded access position in a region, the
+populated size (or amount of written data) in a region along with the size of
+the region. For a writing endpoint, the position and populated size will be
+the same.
 
 Navigation to the next available region of the pipe is performed using the
 following operation:
diff -r bbb065eae483 -r 5c24477f91bf libfsclient/include/fsclient/file.h
--- a/libfsclient/include/fsclient/file.h	Fri May 10 14:49:52 2024 +0200
+++ b/libfsclient/include/fsclient/file.h	Fri May 10 19:00:38 2024 +0200
@@ -162,7 +162,7 @@
 
 /* Pipe region operations. */
 
-long pipe_current(file_t *pipe);
+long pipe_current(file_t *pipe, int sync);
 long pipe_next(file_t *pipe);
 long pipe_written(file_t *pipe, offset_t size);
 
diff -r bbb065eae483 -r 5c24477f91bf libfsclient/lib/src/client.cc
--- a/libfsclient/lib/src/client.cc	Fri May 10 14:49:52 2024 +0200
+++ b/libfsclient/lib/src/client.cc	Fri May 10 19:00:38 2024 +0200
@@ -209,7 +209,7 @@
     if (file->object_flags & OBJECT_SUPPORTS_MMAP)
       return client_mmap(file, client_tell(file), count, 0, 0,
                          file_region_flags(file->flags));
-    else if (pipe_current(file))
+    else if (pipe_current(file, 0))
       return NULL;
   }
 
@@ -305,17 +305,16 @@
   return stream;
 }
 
-/* Initialise the stream data position to the end of any existing data. */
+/* Initialise the stream data position to the end of any existing data for an
+   output stream. For an input stream, initialise the position to the end of
+   consumed data, preserving any unconsumed data. */
 
 long client_sync_stream(file_t *file)
 {
-  long err = client_current_region(file);
+  if (!client_opened(file))
+    return -L4_EINVAL;
 
-  if (err)
-    return err;
-
-  file->data_current = file->data_end;
-  return err;
+  return pipe_current(file, 1);
 }
 
 
@@ -558,24 +557,15 @@
 
 
 
-/* Obtain the current region of a pipe. */
+/* Obtain the current region of a pipe, updating the extent of populated data
+   and only changing the current position if no populated data exists. */
 
 long client_current_region(file_t *file)
 {
   if (!client_opened(file))
     return -L4_EINVAL;
 
-  long err = pipe_current(file);
-
-  if (err)
-    return err;
-
-  /* Handle any case where the current region has been exhausted. */
-
-  if (!file_populated_span(file))
-    file->data_current = 0;
-
-  return L4_EOK;
+  return pipe_current(file, 0);
 }
 
 
@@ -616,13 +606,7 @@
   if (!client_opened(file))
     return -L4_EINVAL;
 
-  long err = pipe_next(file);
-
-  if (err)
-    return err;
-
-  file->data_current = 0;
-  return L4_EOK;
+  return pipe_next(file);
 }
 
 
diff -r bbb065eae483 -r 5c24477f91bf libfsclient/lib/src/file.cc
--- a/libfsclient/lib/src/file.cc	Fri May 10 14:49:52 2024 +0200
+++ b/libfsclient/lib/src/file.cc	Fri May 10 19:00:38 2024 +0200
@@ -680,16 +680,27 @@
 
 /* Access the current region for a pipe endpoint. */
 
-long pipe_current(file_t *pipe)
+long pipe_current(file_t *pipe, int sync)
 {
   client_Pipe _pipe(pipe->ref);
-  long err = _pipe.current_region(&pipe->data_end, &pipe->size);
+  offset_t data_current;
+  long err = _pipe.current_region(&data_current, &pipe->data_end, &pipe->size);
 
   if (err)
     return err;
 
   pipe->end_pos = pipe->size;
 
+  /* Obtain the current position if synchronising position state. */
+
+  if (sync)
+    pipe->data_current = data_current;
+
+  /* Handle any case where the current region has been exhausted. */
+
+  if (!file_populated_span(pipe))
+    pipe->data_current = 0;
+
   /* Attach memory if necessary. */
 
   if (pipe->memory == NULL)
@@ -720,6 +731,7 @@
     return err;
 
   pipe->end_pos = pipe->size;
+  pipe->data_current = 0;
   pipe->memory = NULL;
 
   err = ipc_attach_dataspace(pipe->ref, file_span(pipe), (void **) &pipe->memory);
diff -r bbb065eae483 -r 5c24477f91bf libfsserver/include/fsserver/file_pager.h
--- a/libfsserver/include/fsserver/file_pager.h	Fri May 10 14:49:52 2024 +0200
+++ b/libfsserver/include/fsserver/file_pager.h	Fri May 10 19:00:38 2024 +0200
@@ -1,7 +1,7 @@
 /*
  * File-specific pager functionality.
  *
- * Copyright (C) 2021, 2022, 2023 Paul Boddie <paul@boddie.org.uk>
+ * Copyright (C) 2021, 2022, 2023, 2024 Paul Boddie <paul@boddie.org.uk>
  *
  * This program is free software; you can redistribute it and/or
  * modify it under the terms of the GNU General Public License as
@@ -63,7 +63,7 @@
 
     /* File methods. */
 
-    virtual long flush(offset_t populated_size, offset_t *size);
+    virtual long flush(offset_t position, offset_t *size);
 
     virtual long reopen(flags_t flags, offset_t *size, l4_cap_idx_t *file,
                         object_flags_t *object_flags);
diff -r bbb065eae483 -r 5c24477f91bf libfsserver/include/fsserver/pager.h
--- a/libfsserver/include/fsserver/pager.h	Fri May 10 14:49:52 2024 +0200
+++ b/libfsserver/include/fsserver/pager.h	Fri May 10 19:00:38 2024 +0200
@@ -1,7 +1,7 @@
 /*
  * Generic pager functionality.
  *
- * Copyright (C) 2021, 2022 Paul Boddie <paul@boddie.org.uk>
+ * Copyright (C) 2021, 2022, 2024 Paul Boddie <paul@boddie.org.uk>
  *
  * This program is free software; you can redistribute it and/or
  * modify it under the terms of the GNU General Public License as
@@ -53,7 +53,7 @@
 
     /* File methods. */
 
-    virtual long flush(offset_t populated_size, offset_t *size);
+    virtual long flush(offset_t position, offset_t *size);
 
     virtual long resize(offset_t *size);
 
diff -r bbb065eae483 -r 5c24477f91bf libfsserver/include/fsserver/pipe_pager.h
--- a/libfsserver/include/fsserver/pipe_pager.h	Fri May 10 14:49:52 2024 +0200
+++ b/libfsserver/include/fsserver/pipe_pager.h	Fri May 10 19:00:38 2024 +0200
@@ -35,6 +35,7 @@
 protected:
     PipePaging *_paging;
     bool _writing;
+    offset_t _data_current;
     l4_cap_idx_t _notifier = L4_INVALID_CAP;
 
     /* Helper methods. */
@@ -65,13 +66,13 @@
 
     virtual long closed(int *closed);
 
-    virtual long current_region(offset_t *populated_size, offset_t *size);
+    virtual long current_region(offset_t *position, offset_t *populated_size, offset_t *size);
 
     virtual long next_region(offset_t *populated_size, offset_t *size);
 
     /* Flushing/synchronisation. */
 
-    virtual long flush(offset_t populated_size, offset_t *size);
+    virtual long flush(offset_t position, offset_t *size);
 
     /* Notification methods. */
 
diff -r bbb065eae483 -r 5c24477f91bf libfsserver/lib/files/file_pager.cc
--- a/libfsserver/lib/files/file_pager.cc	Fri May 10 14:49:52 2024 +0200
+++ b/libfsserver/lib/files/file_pager.cc	Fri May 10 19:00:38 2024 +0200
@@ -1,7 +1,7 @@
 /*
  * File-specific pager functionality.
  *
- * Copyright (C) 2021, 2022, 2023 Paul Boddie <paul@boddie.org.uk>
+ * Copyright (C) 2021, 2022, 2023, 2024 Paul Boddie <paul@boddie.org.uk>
  *
  * This program is free software; you can redistribute it and/or
  * modify it under the terms of the GNU General Public License as
@@ -64,9 +64,9 @@
 
 /* File-specific operations. */
 
-long FilePager::flush(offset_t populated_size, offset_t *size)
+long FilePager::flush(offset_t position, offset_t *size)
 {
-    long err = Pager::flush(populated_size, size);
+    long err = Pager::flush(position, size);
 
     if (_resized)
     {
diff -r bbb065eae483 -r 5c24477f91bf libfsserver/lib/generic/pager.cc
--- a/libfsserver/lib/generic/pager.cc	Fri May 10 14:49:52 2024 +0200
+++ b/libfsserver/lib/generic/pager.cc	Fri May 10 19:00:38 2024 +0200
@@ -1,7 +1,7 @@
 /*
  * Generic pager functionality.
  *
- * Copyright (C) 2021, 2022, 2023 Paul Boddie <paul@boddie.org.uk>
+ * Copyright (C) 2021, 2022, 2023, 2024 Paul Boddie <paul@boddie.org.uk>
  *
  * This program is free software; you can redistribute it and/or
  * modify it under the terms of the GNU General Public License as
@@ -59,9 +59,9 @@
 
 /* Flush data to the file. */
 
-long Pager::flush(offset_t populated_size, offset_t *size)
+long Pager::flush(offset_t position, offset_t *size)
 {
-    _mapper->flush_all(_start, populated_size);
+    _mapper->flush_all(_start, position);
 
     *size = _mapper->get_data_size();
     return L4_EOK;
diff -r bbb065eae483 -r 5c24477f91bf libfsserver/lib/pipes/pipe_pager.cc
--- a/libfsserver/lib/pipes/pipe_pager.cc	Fri May 10 14:49:52 2024 +0200
+++ b/libfsserver/lib/pipes/pipe_pager.cc	Fri May 10 19:00:38 2024 +0200
@@ -36,6 +36,10 @@
 
     _size = _paging->region_size();
 
+    /* Initialise any recorded position in the region. */
+
+    _data_current = 0;
+
     /* Obtain any initial page mapper, this having been set up in the paging
        coordinator. */
 
@@ -92,10 +96,13 @@
 
 /* Return details of the current region. */
 
-long PipePager::current_region(offset_t *populated_size, offset_t *size)
+long PipePager::current_region(offset_t *position, offset_t *populated_size, offset_t *size)
 {
     if (_mapper != NULL)
     {
+        if (position != NULL)
+            *position = _data_current;
+
         *populated_size = _mapper->get_data_size();
         *size = _size;
         return L4_EOK;
@@ -124,8 +131,9 @@
         return pipe_error();
 
     _mapper = mapper;
+    _data_current = 0;
 
-    return current_region(populated_size, size);
+    return current_region(NULL, populated_size, size);
 }
 
 long PipePager::next_region_for_writer(offset_t *populated_size, offset_t *size)
@@ -143,8 +151,9 @@
         return pipe_error();
 
     _mapper = mapper;
+    _data_current = 0;
 
-    return current_region(populated_size, size);
+    return current_region(NULL, populated_size, size);
 }
 
 long PipePager::pipe_error()
@@ -157,12 +166,19 @@
 
 
 
-/* Update the populated size of a pipe region and notify the other endpoint. */
+/* Update the consumed or populated size of a pipe region and notify the other
+   endpoint. The consumed size is recorded to allow pipes to be shared between
+   programs. */
 
-long PipePager::flush(offset_t populated_size, offset_t *size)
+long PipePager::flush(offset_t position, offset_t *size)
 {
-    if (_writing && (_mapper != NULL))
-        _mapper->set_data_size(populated_size);
+    if (_mapper != NULL)
+    {
+        _data_current = position;
+
+        if (_writing)
+            _mapper->set_data_size(position);
+    }
 
     *size = _size;
 
diff -r bbb065eae483 -r 5c24477f91bf libsystypes/idl/flush.idl
--- a/libsystypes/idl/flush.idl	Fri May 10 14:49:52 2024 +0200
+++ b/libsystypes/idl/flush.idl	Fri May 10 19:00:38 2024 +0200
@@ -4,7 +4,9 @@
 
 interface Flush
 {
-  /* Flush data and update the size, if appropriate. */
+  /* Flush data and update the size, if appropriate. When writing, the position
+     indicates the populated size of the object; when reading, the position
+     indicates the point from which data is being consumed by a client. */
 
-  [opcode(5)] void flush(in offset_t populated_size, out offset_t size);
+  [opcode(5)] void flush(in offset_t position, out offset_t size);
 };
diff -r bbb065eae483 -r 5c24477f91bf libsystypes/idl/pipe.idl
--- a/libsystypes/idl/pipe.idl	Fri May 10 14:49:52 2024 +0200
+++ b/libsystypes/idl/pipe.idl	Fri May 10 19:00:38 2024 +0200
@@ -6,7 +6,7 @@
 {
   /* Obtain details of the current region of shared memory. */
 
-  [opcode(16)] void current_region(out offset_t populated_size, out offset_t size);
+  [opcode(16)] void current_region(inout offset_t position, out offset_t populated_size, out offset_t size);
 
   /* Advance to the next region of shared memory, indicating and obtaining the
      populated limit of the region and obtaining the region size. */