Re: Write USB Device Driver entry not called

[Raj <inguva@gmail.com>]

On Sat, 23 Oct 2004 07:12:56 +0530, eshwar <eshwar@moschip.com> wrote:
> I agree but the return value from the vfs_write should not be the -EBADF
> (Bad File descriptor) it might be -EACCES (premission denied)... Correct me
> if I am wrong...
> 
> this can be code in fs/read_write.c vfs_write()
> 
>  if (!(file->f_mode & FMODE_WRITE))
>   return -EACCES;

Wrong. You are confused between file perms & mode of access to files. 
If you cannot open a file due to insufficient perms, then EACCESS is
what you get.
If you opened a file for reading, but you tried to write, the you get a EBADF.

Run the following code, after you create two files, 'foo' ( perms 0400
) and 'bar' ( 0700 ).

#include <fcntl.h>

int main()
{
        int fd;

        fd = open("foo",O_WRONLY);

        if(fd < 0)
                perror("Opening foo:");
        else
                close (fd);

        fd = open("bar",O_RDONLY);

        if(fd < 0)
                perror("Opening bar: ");
        else {
                if(write(fd,'a',1) < 0)
                        perror("Write to bar failed: ");
                close(fd);
        }

}

Output would be:
Opening foo:: Permission denied
Write to bar failed: : Bad file descriptor
-- 
######
raj
######