When does the /dev/sda1 node comes into being ?

[Peter Teoh]

i think it depends.   some are softlinks in /dev/ some are created by udev
after udevd read the configuration file, many scenario involved (just
search for "util_create_path" inside udev source codes and u can what are
all the situation).

but for harddisk (whose partition is also the rootfs) /dev/sda is created
during kernel booting up (inside the initrd file, just gunzip and extract
out the cpio file, eg, view the file scripts/local and u can see it make
the /dev/sdXXXX nodes based on /sys/block/XXXX information, which in turn
depends on the kernel calling xxxx_device_register() functions (there a few
variations of them - organized hierarchically)).

on the other hand, if /dev/sda is not the rootfs, but just a normal
harddisk listed in /etc/fstab, then likely it is mounted by udev, detecting
it, and then calling (indirectly from userspace to kernel)
sd_probe_async(), which will then printk() out the "Write Protect is off"
message in your dmesg output - anytime u plug in the harddisk u can see
this.

On Wed, Feb 6, 2013 at 1:26 AM, horseriver <horserivers at gmail.com> wrote:

> hi:)
>
>   During booting period .every device will have a node at /dev/ folder.
>   what is the detail of ths procedure?
>
> thanks!
>
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-- 
Regards,
Peter Teoh
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