A simple sendfile program, but not works

Question

#include <unistd.h>
#include <stdio.h>
#include <string.h>
#include <sys/sendfile.h>
#include <sys/stat.h>
#include <fcntl.h>

int main(){
    int fd1,fd2,rc;
    off_t offset = 0;
    struct stat stat_buf;

    fd1=open("./hello.txt",O_RDONLY); //read only
    fd2=open("../",O_RDWR);           //both read and write
    fstat(fd1, &stat_buf);            //get the size of hello.txt
    printf("file size: %d\n",(int)stat_buf.st_size);
    rc=sendfile (fd2, fd1, &offset, stat_buf.st_size);
}

So as you have seen, it's quite a simple program. But I just can't find hello.txt in ../ My aim is to see what happens if I put a whatever number, says 10, instead of st_size which may be hundreds of bytes.

Edit:

Thanks for your answers. Well, I followed your advice and changed

 fd2=open("../",O_RDWR);

to

 fd2=open("../hello.txt",O_RDWR);

Also, I checked the return value of fstat and sendfile, everything is ok.

But the problem is still the same.

have you checked that hello.txt is excites in previous folder.? — Jeegar Patel, Oct 05 '11 at 10:37
Hi @Mr.32 , did you mean exists? Well, the results shows that hello.txt won't be created in the previous folder. — sliter, Oct 05 '11 at 11:37
in previous folder there should be hello.txt which you are going to open.. — Jeegar Patel, Oct 05 '11 at 11:40
well, I've also tried to creat a hello.txt manually or by just using O_RDWR|O_CREAT. So I can find the file there but it's just an empty file. — sliter, Oct 05 '11 at 13:20

score 2 · Answer 1 · answered Oct 05 '11 at 09:26

2

You need to specify the filename in the second open, not just the directory name.

Please be sure to check the return values of all these functions, including fstat.

answered Oct 05 '11 at 09:26

Mat

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score 2 · Answer 2 · answered Oct 05 '11 at 09:26

2

Have you tried fd2 = open("../hello.txt",O_RDWR);?

answered Oct 05 '11 at 09:26

CharlesB

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Hi @CharlesB, I've followed your advice but the result is still the same – sliter Oct 05 '11 at 11:38

Jeegar Patel · Accepted Answer · 2011-10-05T09:44:55.177

1>

  fd1=open("./hello.txt",O_RDONLY); //read only
  fd2=open("../",O_RDWR);           //both read and write

replace with

 fd1=open("../hello.txt",O_RDONLY); //read only
  fd2=open("../your_file_name",O_RDWR);

2>

 fstat(fd1, &stat_buf);

will fill up some info related to fd1 file in stat_buf . Here size of that file is also return in that structure with st_size element.

now in

 rc=sendfile (fd2, fd1, &offset, stat_buf.st_size);

total stat_buf.st_size bytes are going to send on fd2 file. if here if you write 10 then only 10 bytes will go in fd2.

A simple sendfile program, but not works

3 Answers3