how to know the Interrupt/GPIO number for a specific pin in linux

The Embedded Linux you are using should have a GPIO driver that has #define statements for the GPIO pins. You can then get the IRQ number of the specific GPIO using something like:

irq_num = gpio_to_irq(S3C64XX_GPP(8));

The Linux GPIO lib support for that particular chip is available in the following file:

linux/arch/arm/mach-s3c6400/include/mach/gpio.h

There you will find all the #define statements for the various GPIO.

See the section on GPIO Conventions in their documentation:

http://www.kernel.org/doc/Documentation/gpio/gpio.txt