$ cat a.c

#include <sys/sendfile.h>

#include <sys/types.h>

#include <sys/stat.h>

#include <fcntl.h>



int main()

{

        int s = open("/boot/vmlinuz-2.4.21-20.EL", O_RDONLY);

        int d = open("output", O_WRONLY | O_CREAT, 0600);

        off_t off = 0;

        ssize_t size = sendfile(d, s, &off, 10000000);

        printf("size = %d, off = %d
", size, off);

}



$ ./a

size = 1243768, off = 1243768



$ md5sum output /boot/vmlinuz-2.4.21-20.EL

a7a6a1d88660615f357fef276140ddd7  output

a7a6a1d88660615f357fef276140ddd7  /boot/vmlinuz-2.4.21-20.EL

$ strace ./a >/dev/null

execve("./a", ["./a"], [/* 28 vars */]) = 0

uname({sys="Linux", node="linux", ...}) = 0

brk(0)                                  = 0x86da000

open("/etc/ld.so.preload", O_RDONLY)    = 3

fstat64(3, {st_mode=S_IFREG|0644, st_size=17, ...}) = 0

old_mmap(NULL, 17, PROT_READ|PROT_WRITE, MAP_PRIVATE, 3, 0) = 0xb75f7000

close(3)                                = 0

open("/etc/libcwait.so", O_RDONLY)      = 3

read(3, "177ELF1113313404"..., 512) = 512

fstat64(3, {st_mode=S_IFREG|0755, st_size=4431, ...}) = 0

old_mmap(NULL, 5912, PROT_READ|PROT_EXEC, MAP_PRIVATE, 3, 0) = 0x61e000

old_mmap(0x61f000, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED, 3, 0) =

0x61f000

close(3)                                = 0

munmap(0xb75f7000, 17)                  = 0

open("/etc/ld.so.cache", O_RDONLY)      = 3

fstat64(3, {st_mode=S_IFREG|0644, st_size=86552, ...}) = 0

old_mmap(NULL, 86552, PROT_READ, MAP_PRIVATE, 3, 0) = 0xb75e2000

close(3)                                = 0

open("/lib/tls/libc.so.6", O_RDONLY)    = 3

read(3, "177ELF111331200X1"..., 512) = 512

old_mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) =

0xb75e1000

fstat64(3, {st_mode=S_IFREG|0755, st_size=1568924, ...}) = 0

old_mmap(NULL, 1276876, PROT_READ|PROT_EXEC, MAP_PRIVATE, 3, 0) = 0x111000

old_mmap(0x243000, 16384, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED, 3, 0x131000) =

0x243000

old_mmap(0x247000, 7116, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_ANONYMOUS,

-1, 0) = 0x247000

close(3)                                = 0

set_thread_area({entry_number:-1 -> 6, base_addr:0xb75e17c0, limit:1048575,

seg_32bit:1, contents:0, read_exec_only:0, limit_in_pages:1, seg_not_present:0,

useable:1}) = 0

munmap(0xb75e2000, 86552)               = 0

open("/boot/vmlinuz-2.4.21-20.EL", O_RDONLY) = 3

open("output", O_WRONLY|O_CREAT, 0600)  = 4

sendfile(4, 3, [0], 10000000)           = 1243768

fstat64(1, {st_mode=S_IFCHR|0666, st_rdev=makedev(1, 3), ...}) = 0

ioctl(1, SNDCTL_TMR_TIMEBASE or TCGETS, 0xbfffb950) = -1 ENOTTY (Inappropriate ioctl

for device)

mmap2(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) =

0xb75f7000

write(1, "size = 1243768, off = 1243768
", 30) = 30

munmap(0xb75f7000, 4096)                = 0

exit_group(30)                          = ?