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

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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>
This commit is contained in:
Bartosz Golaszewski 2014-11-27 13:20:24 +01:00 committed by Denys Vlasenko
parent ee41094b80
commit 8d75d794ea
4 changed files with 71 additions and 42 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

12
Config.in
View File

@ -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

77
libbb/copyfd.c
View File

@ -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) {
@ -31,7 +46,29 @@ static off_t bb_full_fd_action(int src_fd, int dst_fd, off_t size)
continue_on_write_error = 1;
}
if (src_fd < 0)
goto out;
sendfile_sz = !ENABLE_FEATURE_USE_SENDFILE
? 0
: SENDFILE_BIGBUF;
if (!size) {
size = SENDFILE_BIGBUF;
status = 1; /* copy until eof */
}
while (1) {
ssize_t rd;
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
@ -46,31 +83,21 @@ static off_t bb_full_fd_action(int src_fd, int dst_fd, off_t size)
buffer = alloca(4 * 1024);
buffer_size = 4 * 1024;
}
}
#endif
if (src_fd < 0)
goto out;
if (!size) {
size = buffer_size;
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;
}
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;
}

8
networking/Config.src
View File

@ -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

6
networking/httpd.c
View File

@ -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");
}