Casper.Dik at Sun.COM wrote:
>> Hi!
>>
>> ----
>>
>> Is there a way to detect whether a fd refers to "/dev/null" based on the
>> return values of |stat()| ?
>
> Sure, stat("/dev/null") and compare the fields:
>
> st_mode (the type of the file, must be a char device)
>
> st_rdev (the major, minor of the device), note: "st_*r*dev", not
> st_dev.
Remember that /dev/null is a symlink though. So Ideally do an open(2) [
and *don't* specify O_NOFOLLOW] then fstat it.
Or given Roland asked about an existing fd just fstat.
This is the type of info you will get:
portellen:pts/2$ stat /dev/null
File: `/dev/null' -> `../devices/pseudo/mm at 0:null'
Size: 27 Blocks: 1 IO Block: 512 symbolic link
Device: 5400000h/88080384d Inode: 1522315013 Links: 1
Access: (0777/lrwxrwxrwx) Uid: ( 0/ root) Gid: ( 0/ root)
Access: 2009-09-17 16:41:22.256354770 +0100
Modify: 2009-07-27 10:53:27.691048106 +0100
Change: 2009-07-27 10:53:27.691081044 +0100
portellen:pts/2$ stat -L /dev/null
File: `/dev/null'
Size: 0 Blocks: 0 IO Block: 8192 character
special file
Device: 53c0000h/87818240d Inode: 6815752 Links: 1 Device type: d,2
Access: (0666/crw-rw-rw-) Uid: ( 0/ root) Gid: ( 3/ sys)
Access: 2009-09-09 10:37:22.000000000 +0100
Modify: 2009-09-17 16:00:01.000000000 +0100
Change: 2009-09-03 13:18:40.000000000 +0100
That doesn't tell it is /dev/null but as Casper said it tells you the
device type.
--
Darren J Moffat
