Getting file type from inode of fd

Getting file type from inode of fd

[Peter Chen]

Hi,

  I was wondering, how I can tell a file is a regular file ("-" when
you run ls -l) or a socket ("s" when you run ls -l). I think I can use
sockfd_lookup on the fd to check if a fd points to a socket (NULL if
it doesn't).

   But I see these macros in stat.h (S_ISREG, S_ISSOCK) that takes an
inode's umode and returns true if the inode is a specific file type.
But I was wondering, if I use fget() to get the file of a fd, can I
get the inode from the file from f_inode? I see the comment says it is
a cached value. So what would go wrong if I went something like
S_ISREG(file->f_inode) or is this the correct way to do this?

Peter

Re: Getting file type from inode of fd

[Jan Kara]

Hi,

On Sun 24-07-16 20:19:59, Peter Chen wrote:
>   I was wondering, how I can tell a file is a regular file ("-" when
> you run ls -l) or a socket ("s" when you run ls -l). I think I can use
> sockfd_lookup on the fd to check if a fd points to a socket (NULL if
> it doesn't).
> 
>    But I see these macros in stat.h (S_ISREG, S_ISSOCK) that takes an
> inode's umode and returns true if the inode is a specific file type.
> But I was wondering, if I use fget() to get the file of a fd, can I
> get the inode from the file from f_inode? I see the comment says it is
> a cached value. So what would go wrong if I went something like
> S_ISREG(file->f_inode) or is this the correct way to do this?

You can use file_inode() helper and then S_ISREG() function to test file
type. That is certainly going to work.

								Honza
-- 
Jan Kara <jack@suse.com>
SUSE Labs, CR