Introduce FEATURE_COPYBUF_KB.

People who want smaller stack at any cost may use it
to reduce cp's stack usage (FEATURE_COPYBUF_KB=1).
Desktop people may get faster copy of big files
(FEATURE_COPYBUF_KB=32 is ~30% faster than 4kb)

2 files changed, 34 insertions, 8 deletions

diff --git a/libbb/Config.in b/libbb/Config.in
index 5055015cf..6bbeffb43 100644
--- a/libbb/Config.in
+++ b/libbb/Config.in
@@ -110,6 +110,16 @@ config FEATURE_EDITING_FANCY_PROMPT
           Setting this option allows for prompts to use things like \w and
           \$ and escape codes.
 
+config FEATURE_COPYBUF_KB
+        int "Copy buffer size, in kilobytes"
+        range 1 1024
+        default 4
+        help
+          Size of buffer used by cp, mv, install etc.
+          Buffers which are 4 kb or less will be allocated on stack.
+          Bigger buffers will be allocated with mmap, with fallback to 4 kb
+          stack buffer if mmap fails.
+
 config MONOTONIC_SYSCALL
         bool "Use clock_gettime(CLOCK_MONOTONIC) syscall"
         default y
diff --git a/libbb/copyfd.c b/libbb/copyfd.c
index 3255e424a..ed383ae28 100644
--- a/libbb/copyfd.c
+++ b/libbb/copyfd.c
@@ -9,31 +9,42 @@
 
 #include "libbb.h"
 
-#if BUFSIZ < 4096
-#undef BUFSIZ
-#define BUFSIZ 4096
-#endif
-
 /* Used by NOFORK applets (e.g. cat) - must not use xmalloc */
 
 static off_t bb_full_fd_action(int src_fd, int dst_fd, off_t size)
 {
         int status = -1;
         off_t total = 0;
-        char buffer[BUFSIZ];
+#if CONFIG_FEATURE_COPYBUF_KB <= 4
+        char buffer[CONFIG_FEATURE_COPYBUF_KB * 1024];
+        enum { buffer_size = sizeof(buffer) };
+#else
+        char *buffer;
+        int buffer_size;
+
+        buffer = mmap(NULL, CONFIG_FEATURE_COPYBUF_KB * 1024,
+                        PROT_READ | PROT_WRITE,
+                        MAP_PRIVATE | MAP_ANON,
+                        /* ignored: */ -1, 0);
+        buffer_size = CONFIG_FEATURE_COPYBUF_KB * 1024;
+        if (buffer == MAP_FAILED) {
+                buffer = alloca(4 * 1024);
+                buffer_size = 4 * 1024;
+        }
+#endif
 
         if (src_fd < 0)
                 goto out;
 
         if (!size) {
-                size = BUFSIZ;
+                size = buffer_size;
                 status = 1; /* copy until eof */
         }
 
         while (1) {
                 ssize_t rd;
 
-                rd = safe_read(src_fd, buffer, size > BUFSIZ ? BUFSIZ : size);
+                rd = safe_read(src_fd, buffer, size > buffer_size ? buffer_size : size);
 
                 if (!rd) { /* eof - all done */
                         status = 0;
@@ -62,6 +73,11 @@ static off_t bb_full_fd_action(int src_fd, int dst_fd, off_t size)
                 }
         }
  out:
+
+#if CONFIG_FEATURE_COPYBUF_KB > 4
+        if (buffer_size != 4 * 1024)
+                munmap(buffer, buffer_size);
+#endif
         return status ? -1 : total;
 }