if I modify the code like this
char abc;
if(read(fd,&abc,1) < 0)
perror("read to bar failed: ");
close(fd);
Which will be sucess... This intern states that my file descriptor is right
.... but write returns EBADF... both are contradicting statements....
Eshwar
----- Original Message -----
From: "Raj" <[email protected]>
To: "eshwar" <[email protected]>
Cc: "Alan Cox" <[email protected]>; "Linux Kernel Mailing List"
<[email protected]>
Sent: Thursday, October 14, 2004 9:09 AM
Subject: Re: Write USB Device Driver entry not called
> On Sat, 23 Oct 2004 07:12:56 +0530, eshwar <[email protected]> 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
> ######
> -
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On Thu, 21 Oct 2004 09:24:52 +0530, eshwar <[email protected]> wrote:
> if I modify the code like this
>
> char abc;
> if(read(fd,&abc,1) < 0)
> perror("read to bar failed: ");
> close(fd);
>
> Which will be sucess... This intern states that my file descriptor is right
> .... but write returns EBADF... both are contradicting statements....
It's this simple. File was opened for Read-Only. So for vfs_read it is
a 'good' file
descriptor. And for vfs_write it is a 'BAD' file descriptor.
--
######
raj
######