Thanks Sri Ram and Jonathan,
On Wed, Apr 25, 2012 at 11:39 PM, Sri Ram Vemulpali
<sri.ram.gmu06@xxxxxxxxx> wrote:
> Ok I see your problem.
>
> vfs maintains file descriptor table for every process in the system.
> At every index it stores information of descriptor type and device it
> points to. The indexes 0,1,2 have special meaning in the context of
> process. 0 indicates std input, 1 indicates std output and 2 indicates
> std err.
> So whenever you use open(), socket(), or any other system call which
> returns descriptor (expect fopen .. libc functions) is returning the
> index in to this table where the info about device or operation is
> stored. So, whenever you use that descriptor number with other sys
> calls it will map in to index and extracts the information.
>
> normal calls like printf, cout uses "stdin, stdout, stderr" for printing out.
>
>> We all know that when an application writes to stdout, data ends up in
>> the console.
> Because for that process index 1 maps to /dev/stdout
>
>> Okey so if I m on my development board and if I run an app, all the
>> prints comes to the console (eg /dev/ttyS0).
> same as above
>
>> If I m on any server using ssh and all apps prints comes on my putty
>> (eg through /dev/pts/176).
> its ssh implementation. It uses pty as stdout for printing.
Okey
> In such case initializing stdout = fdopen on open("/dev/stdout", "")
> descriptor will do your job.
> or use dup to set index 1 to given fd in that process
Hmm... Will sshd open /dev/stdout?
I think it uses /dev/ptmx and /dev/pts/* device files.
Plz have a look here,
http://linux.die.net/man/4/pts
Arun
>
>
> --Sri.
>
> On Mon, Apr 23, 2012 at 6:15 AM, Arun KS <getarunks@xxxxxxxxx> wrote:
>> Hello Guys,
>>
>> We all know that when an application writes to stdout, data ends up in
>> the console.
>>
>> Okey so if I m on my development board and if I run an app, all the
>> prints comes to the console (eg /dev/ttyS0).
>> If I m on any server using ssh and all apps prints comes on my putty
>> (eg through /dev/pts/176).
>>
>> Where is the code which maps fd 1 to the console in kernel?
>> If you guys have any pointers, please share.
>>
>> While opening a device (for eg /dev/something), the vfs calls that
>> drivers, whose major and minor number matches.
>> But in case of stdout, how vfs resolves the write to the fd 1 and send
>> it to the corresponding console driver?
>>
>> Thanks,
>> Arun
>>
>> _______________________________________________
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>
>
>
> --
> Regards,
> Sri.
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