Re: Finding size of a raw device

[Learner <ruxyz@xxxxxxxxx>]

Hi ,

 Probably I found the answer to this . 

On a filesystem, by doing an lseek the OS can 
track the size of the file via the inodes .

Thus, an lseek with SEEK_END would give the 
file size , as the inode tables provide the 
needed support for the OS .

But since a raw device bound to a file is a 
direct interface , there is no way in which 
the OS can figure out its limits , and thus 
lseek with SEEK_END would yield a zero .

It would be nice if somebody could confirm 
the above explanation .

Cheers !

 --- Learner <ruxyz@xxxxxxxxx> wrote: > Hi ,
> 
>   I was trying to find the size of a raw partition 
> using the below program , but the output is not 
> correct. Can anybody suggest how to rectify this
> program.
> 
>   Is it that "lseek" should be used only on regular 
> files and not special files ?Is there a proc entry 
> which reflects the currently bound raw devices ?
> 
>    I'am aware that "raw -qa" gives the complete list
> of raw devices , but I wanted to know if there is 
> any other method to do so .
> 
> 
> PROGRAM :-
> 
> #include <sys/types.h>
> #include <sys/stat.h>
> #include <fcntl.h>
> #include <unistd.h>
> 
> main()
> {
>    int fd ;
>    int start, end ;
> 
>    fd=open( "/dev/raw/raw1", O_RDONLY );
> 
>    start=lseek( fd, 0, SEEK_SET );
> 
>    printf("The Start pt size is %d \n", start);
> 
>    end=lseek( fd, 0, SEEK_END );
> 
>    printf("The End pt size is %d \n", end);
> }
> 
> OUTPUT :-
> 
> The Start pt size is 0
> The End pt size is 0
> 
> 
> Cheers!
> 
> 
>
________________________________________________________________________
> Yahoo! India Matrimony: Find your partner online.
> http://yahoo.shaadi.com/india-matrimony/
> 
> --
> Kernelnewbies: Help each other learn about the Linux
> kernel.
> Archive:      
> http://mail.nl.linux.org/kernelnewbies/
> FAQ:           http://kernelnewbies.org/faq/
>  

________________________________________________________________________
Yahoo! India Matrimony: Find your partner online. http://yahoo.shaadi.com/india-matrimony/

--
Kernelnewbies: Help each other learn about the Linux kernel.
Archive:       http://mail.nl.linux.org/kernelnewbies/
FAQ:           http://kernelnewbies.org/faq/