libbb: use sendfile() to copy data between file descriptors

Busybox already uses sendfile in httpd. This patch proposes to use it
globally to copy data between file descriptors.

It speeds up the copying on slow systems a lot - below are the times needed
to copy a 450Mb file with and without this option enabled on a BeagleBone
Black:

sendfile:
user    0m0.000s
sys     0m8.170s

read/write 4k:
user    0m0.470s
sys     0m16.300s

function                                             old     new   delta
bb_full_fd_action                                    394     474     +80

Signed-off-by: Bartosz Golaszewski <bartekgola@gmail.com>
Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>

diff --git a/Config.in b/Config.in
index b83beb52dfc14c7eaa945f2f9d166aa277653969..285fe0a19ada2d453a7cd4bf94a41fa7aeb0fea0 100644 (file)
--- a/Config.in
+++ b/Config.in
@@ -264,6 +264,18 @@ config PAM
          Use PAM in some busybox applets (currently login and httpd) instead
          of direct access to password database.
 
+config FEATURE_USE_SENDFILE
+       bool "Use sendfile system call"
+       default y
+       help
+         When enabled, busybox will use the kernel sendfile() function
+         instead of read/write loops to copy data between file descriptors
+         (for example, cp command does this a lot).
+         If sendfile() doesn't work, copying code falls back to read/write
+         loop. sendfile() was originally implemented for faster I/O
+         from files to sockets, but since Linux 2.6.33 it was extended
+         to work for many more file types.
+
 config LONG_OPTS
        bool "Support for --long-options"
        default y

diff --git a/libbb/copyfd.c b/libbb/copyfd.c
index eda2747f991b0253b8fe3596d79035a5c373dff3..7e353190372260f32627816b2efcd9cd4442a6e2 100644 (file)
--- a/libbb/copyfd.c
+++ b/libbb/copyfd.c
@@ -8,6 +8,20 @@
  */
 
 #include "libbb.h"
+#if ENABLE_FEATURE_USE_SENDFILE
+# include <sys/sendfile.h>
+#else
+# define sendfile(a,b,c,d) (-1)
+#endif
+
+/*
+ * We were using 0x7fff0000 as sendfile chunk size, but it
+ * was seen to cause largish delays when user tries to ^C a file copy.
+ * Let's use a saner size.
+ * Note: needs to be >= max(CONFIG_FEATURE_COPYBUF_KB),
+ * or else "copy to eof" code will use neddlesly short reads.
+ */
+#define SENDFILE_BIGBUF (16*1024*1024)
 
 /* Used by NOFORK applets (e.g. cat) - must not use xmalloc.
  * size < 0 means "ignore write errors", used by tar --to-command
@@ -18,12 +32,13 @@ static off_t bb_full_fd_action(int src_fd, int dst_fd, off_t size)
        int status = -1;
        off_t total = 0;
        bool continue_on_write_error = 0;
-#if CONFIG_FEATURE_COPYBUF_KB <= 4
+       ssize_t sendfile_sz;
+#if CONFIG_FEATURE_COPYBUF_KB > 4
+       char *buffer = buffer; /* for compiler */
+       int buffer_size = 0;
+#else
        char buffer[CONFIG_FEATURE_COPYBUF_KB * 1024];
        enum { buffer_size = sizeof(buffer) };
-#else
-       char *buffer;
-       int buffer_size;
 #endif
 
        if (size < 0) {
@@ -31,46 +46,58 @@ static off_t bb_full_fd_action(int src_fd, int dst_fd, off_t size)
                continue_on_write_error = 1;
        }
 
-#if CONFIG_FEATURE_COPYBUF_KB > 4
-       if (size > 0 && size <= 4 * 1024)
-               goto use_small_buf;
-       /* We want page-aligned buffer, just in case kernel is clever
-        * and can do page-aligned io more efficiently */
-       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) {
- use_small_buf:
-               buffer = alloca(4 * 1024);
-               buffer_size = 4 * 1024;
-       }
-#endif
-
        if (src_fd < 0)
                goto out;
 
+       sendfile_sz = !ENABLE_FEATURE_USE_SENDFILE
+               ? 0
+               : SENDFILE_BIGBUF;
        if (!size) {
-               size = buffer_size;
+               size = SENDFILE_BIGBUF;
                status = 1; /* copy until eof */
        }
 
        while (1) {
                ssize_t rd;
 
-               rd = safe_read(src_fd, buffer, size > buffer_size ? buffer_size : size);
-
-               if (!rd) { /* eof - all done */
-                       status = 0;
-                       break;
+               if (sendfile_sz) {
+                       rd = sendfile(dst_fd, src_fd, NULL,
+                               size > sendfile_sz ? sendfile_sz : size);
+                       if (rd >= 0)
+                               goto read_ok;
+                       sendfile_sz = 0; /* do not try sendfile anymore */
+               }
+#if CONFIG_FEATURE_COPYBUF_KB > 4
+               if (buffer_size == 0) {
+                       if (size > 0 && size <= 4 * 1024)
+                               goto use_small_buf;
+                       /* We want page-aligned buffer, just in case kernel is clever
+                        * and can do page-aligned io more efficiently */
+                       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) {
+ use_small_buf:
+                               buffer = alloca(4 * 1024);
+                               buffer_size = 4 * 1024;
+                       }
                }
+#endif
+               rd = safe_read(src_fd, buffer,
+                       size > buffer_size ? buffer_size : size);
                if (rd < 0) {
                        bb_perror_msg(bb_msg_read_error);
                        break;
                }
+ read_ok:
+               if (!rd) { /* eof - all done */
+                       status = 0;
+                       break;
+               }
                /* dst_fd == -1 is a fake, else... */
-               if (dst_fd >= 0) {
+               if (dst_fd >= 0 && !sendfile_sz) {
                        ssize_t wr = full_write(dst_fd, buffer, rd);
                        if (wr < rd) {
                                if (!continue_on_write_error) {
@@ -92,10 +119,8 @@ 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)
+       if (buffer_size > 4 * 1024)
                munmap(buffer, buffer_size);
-#endif
        return status ? -1 : total;
 }
 

diff --git a/networking/Config.src b/networking/Config.src
index e56646917b3714c9cd27b8ad5774f3d6cc0f8057..15a696876f05d86eedf6fd5389df44892c2ce753 100644 (file)
--- a/networking/Config.src
+++ b/networking/Config.src
@@ -181,14 +181,6 @@ config FEATURE_HTTPD_RANGES
          "Range: bytes=NNN-[MMM]" header. Allows for resuming interrupted
          downloads, seeking in multimedia players etc.
 
-config FEATURE_HTTPD_USE_SENDFILE
-       bool "Use sendfile system call"
-       default y
-       depends on HTTPD
-       help
-         When enabled, httpd will use the kernel sendfile() function
-         instead of read/write loop.
-
 config FEATURE_HTTPD_SETUID
        bool "Enable -u <user> option"
        default y

diff --git a/networking/httpd.c b/networking/httpd.c
index 621d9cddc6aef67b005deb4b8b39725c8d0428b9..9cf0804019ab57064d6fca23451c6fd81f210629 100644 (file)
--- a/networking/httpd.c
+++ b/networking/httpd.c
@@ -133,7 +133,7 @@
 # include <security/pam_appl.h>
 # include <security/pam_misc.h>
 #endif
-#if ENABLE_FEATURE_HTTPD_USE_SENDFILE
+#if ENABLE_FEATURE_USE_SENDFILE
 # include <sys/sendfile.h>
 #endif
 /* amount of buffering in a pipe */
@@ -1624,7 +1624,7 @@ static NOINLINE void send_file_and_exit(const char *url, int what)
 #endif
        if (what & SEND_HEADERS)
                send_headers(HTTP_OK);
-#if ENABLE_FEATURE_HTTPD_USE_SENDFILE
+#if ENABLE_FEATURE_USE_SENDFILE
        {
                off_t offset = range_start;
                while (1) {
@@ -1654,7 +1654,7 @@ static NOINLINE void send_file_and_exit(const char *url, int what)
                        break;
        }
        if (count < 0) {
- IF_FEATURE_HTTPD_USE_SENDFILE(fin:)
+ IF_FEATURE_USE_SENDFILE(fin:)
                if (verbose > 1)
                        bb_perror_msg("error");
        }