From f185581ca3237ec1c37bc4ad92aab4c3ce8e7236 Mon Sep 17 00:00:00 2001
From: Robert Spalek <robert@ucw.cz>
Date: Fri, 25 Jun 2004 12:47:17 +0000
Subject: [PATCH] generalized BCONFIG_CAN_OVERWRITE to three different write
 policies

---
 lib/fastbuf.h   |  9 +++++++++
 lib/fb-buffer.c | 14 +++++++++++++-
 lib/fb-file.c   |  2 +-
 lib/fb-limfd.c  | 13 +++++++++++++
 lib/fb-mem.c    | 14 ++++++++++++++
 lib/fb-mmap.c   |  2 +-
 6 files changed, 51 insertions(+), 3 deletions(-)

diff --git a/lib/fastbuf.h b/lib/fastbuf.h
index 0104a61f..9cc646d3 100644
--- a/lib/fastbuf.h
+++ b/lib/fastbuf.h
@@ -2,6 +2,7 @@
  *	Sherlock Library -- Fast Buffered I/O
  *
  *	(c) 1997--2004 Martin Mares <mj@ucw.cz>
+ *	(c) 2004 Robert Spalek <robert@ucw.cz>
  *
  *	This software may be freely distributed and used according to the terms
  *	of the GNU Lesser General Public License.
@@ -101,6 +102,14 @@ int bconfig(struct fastbuf *f, uns type, int data);
 
 #define BCONFIG_IS_TEMP_FILE 0
 #define BCONFIG_CAN_OVERWRITE 1
+  /* Specified whether the caller is allowed to perform the following optimized
+   * 0-copy write operation:
+   * 	- get the buffer by bdirect_read_prepare()
+   * 	- modify the buffer, e.g. by putting \0's inside
+   * 	- call bflush() to let the fastbuf know
+   * 0: read-only memory
+   * 1: you can write into read-write memory, if you restore the original value
+   * 2: you can rewrite the original content */
 
 /* Universal functions working on all fastbuf's */
 
diff --git a/lib/fb-buffer.c b/lib/fb-buffer.c
index 03c8e321..2e2d4454 100644
--- a/lib/fb-buffer.c
+++ b/lib/fb-buffer.c
@@ -36,6 +36,18 @@ fbbuf_spout(struct fastbuf *f UNUSED)
   die("fbbuf: buffer overflow on write");
 }
 
+static int
+fbbuf_config(struct fastbuf *f UNUSED, uns item, int value UNUSED)
+{
+  switch (item)
+    {
+    case BCONFIG_CAN_OVERWRITE:
+      return 1;
+    default:
+      return -1;
+    }
+}
+
 void
 fbbuf_init_write(struct fastbuf *f, byte *buf, uns size)
 {
@@ -47,5 +59,5 @@ fbbuf_init_write(struct fastbuf *f, byte *buf, uns size)
   f->spout = fbbuf_spout;
   f->seek = NULL;
   f->close = NULL;
-  f->config = NULL;
+  f->config = fbbuf_config;
 }
diff --git a/lib/fb-file.c b/lib/fb-file.c
index abb29ddf..3b416de3 100644
--- a/lib/fb-file.c
+++ b/lib/fb-file.c
@@ -90,7 +90,7 @@ bfd_config(struct fastbuf *f, uns item, int value)
       FB_FILE(f)->is_temp_file = value;
       return 0;
     case BCONFIG_CAN_OVERWRITE:
-      return 1;
+      return 2;
     default:
       return -1;
     }
diff --git a/lib/fb-limfd.c b/lib/fb-limfd.c
index c1b6cb2c..ac95d908 100644
--- a/lib/fb-limfd.c
+++ b/lib/fb-limfd.c
@@ -39,6 +39,18 @@ bfl_close(struct fastbuf *f)
   xfree(f);
 }
 
+static int
+bfl_config(struct fastbuf *f UNUSED, uns item, int value UNUSED)
+{
+  switch (item)
+    {
+    case BCONFIG_CAN_OVERWRITE:
+      return 2;
+    default:
+      return -1;
+    }
+}
+
 struct fastbuf *
 bopen_limited_fd(int fd, uns buflen, uns limit)
 {
@@ -54,6 +66,7 @@ bopen_limited_fd(int fd, uns buflen, uns limit)
   F->limit = limit;
   f->refill = bfl_refill;
   f->close = bfl_close;
+  f->config = bfl_config;
   return f;
 }
 
diff --git a/lib/fb-mem.c b/lib/fb-mem.c
index daa80733..efe749c5 100644
--- a/lib/fb-mem.c
+++ b/lib/fb-mem.c
@@ -149,6 +149,18 @@ fbmem_close(struct fastbuf *f)
   xfree(f);
 }
 
+static int
+fbmem_config(struct fastbuf *f UNUSED, uns item, int value UNUSED)
+{
+  switch (item)
+    {
+    case BCONFIG_CAN_OVERWRITE:
+      return 1;
+    default:
+      return -1;
+    }
+}
+
 struct fastbuf *
 fbmem_create(unsigned blocksize)
 {
@@ -162,6 +174,7 @@ fbmem_create(unsigned blocksize)
   f->name = "<fbmem-write>";
   f->spout = fbmem_spout;
   f->close = fbmem_close;
+  f->config = fbmem_config;
   return f;
 }
 
@@ -179,6 +192,7 @@ fbmem_clone_read(struct fastbuf *b)
   f->refill = fbmem_refill;
   f->seek = fbmem_seek;
   f->close = fbmem_close;
+  f->config = fbmem_config;
   return f;
 }
 
diff --git a/lib/fb-mmap.c b/lib/fb-mmap.c
index f4f90184..bbd3a11e 100644
--- a/lib/fb-mmap.c
+++ b/lib/fb-mmap.c
@@ -161,7 +161,7 @@ bfmm_config(struct fastbuf *f, uns item, int value)
       FB_MMAP(f)->is_temp_file = value;
       return 0;
     case BCONFIG_CAN_OVERWRITE:
-      return 0;
+      return 0;				/* cannot use 1, because the pages would become dirty */
     default:
       return -1;
     }
-- 
2.39.2