Thanks Sri Ram and Jonathan, On Wed, Apr 25, 2012 at 11:39 PM, Sri Ram Vemulpali <sri.ram.gmu06@gmail.com> 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@gmail.com> 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.