busybox/libbb/copyfd.c

/* vi: set sw=4 ts=4: */
/*
 * Utility routines.
 *
 * Copyright (C) 1999-2005 by Erik Andersen <andersen@codepoet.org>
 *
 * Licensed under GPLv2 or later, see file LICENSE in this source tree.
 */
#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
 * size = 0 means "copy till EOF"
 */
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;
	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) };
#endif

	if (size < 0) {
		size = -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
			 * 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 && !sendfile_sz) {
			ssize_t wr = full_write(dst_fd, buffer, rd);
			if (wr < rd) {
				if (!continue_on_write_error) {
					bb_perror_msg(bb_msg_write_error);
					break;
				}
				dst_fd = -1;
			}
		}
		total += rd;
		if (status < 0) { /* if we aren't copying till EOF... */
			size -= rd;
			if (!size) {
				/* 'size' bytes copied - all done */
				status = 0;
				break;
			}
		}
	}
 out:

/* some environments don't have munmap(), hide it in #if */
#if CONFIG_FEATURE_COPYBUF_KB > 4
	if (buffer_size > 4 * 1024)
		munmap(buffer, buffer_size);
#endif
	return status ? -1 : total;
}


#if 0
void FAST_FUNC complain_copyfd_and_die(off_t sz)
{
	if (sz != -1)
		bb_error_msg_and_die("short read");
	/* if sz == -1, bb_copyfd_XX already complained */
	xfunc_die();
}
#endif

off_t FAST_FUNC bb_copyfd_size(int fd1, int fd2, off_t size)
{
	if (size) {
		return bb_full_fd_action(fd1, fd2, size);
	}
	return 0;
}

void FAST_FUNC bb_copyfd_exact_size(int fd1, int fd2, off_t size)
{
	off_t sz = bb_copyfd_size(fd1, fd2, size);
	if (sz == (size >= 0 ? size : -size))
		return;
	if (sz != -1)
		bb_error_msg_and_die("short read");
	/* if sz == -1, bb_copyfd_XX already complained */
	xfunc_die();
}

off_t FAST_FUNC bb_copyfd_eof(int fd1, int fd2)
{
	return bb_full_fd_action(fd1, fd2, 0);
}