svn commit: r321920 - head/sys/sys

[Hans Petter Selasky]

On 08/02/17 13:43, Konstantin Belousov wrote:
> On Wed, Aug 02, 2017 at 01:27:50PM +0200, Hans Petter Selasky wrote:
>> On 08/02/17 13:17, Konstantin Belousov wrote:
>>> But y must be dev_t.
>>
>> Sure, but "struct cdev" 's si_drv0 is only "int" . How can it contain
>> dev_t ?
> 
> Why should it contain dev_t ?
> Linux KPI abused that field it seems.
> 

Hi,

The LinuxKPI uses si_drv0 to contain the output from mkdev(). Before the 
mkdev() function would fit into 32-bits. Now it is 64-bits.

I can fix the LinuxKPI bits this time. We can store this information in 
si_drv1->xxx instead of using si_drv0 and dev2unit().

> Lets change the focus of the discussion.
> You cited the
> struct linux_cdev *
> linux_find_cdev(const char *name, unsigned major, unsigned minor)
> function which finds cdev (or some mockup of the native cdev) by major/minor.
> Where does these major/minor numbers come from ?

The major number is in the range 0..255 and decides the type of device.
The minor number is in the range 0..255 aswell typically and defines a 
unique number for each LinuxKPI created character device.

> I mean that if they are contructed as major(struct stat.st_rdev) and
> minor(struct stat.st_rdev), then even the original code looks wrong
> without the ino64 addition.  Since devfs reports the internal inode
> number into st_rdev, which formally is not accessible outside the devfs
> filesystem.  So should the code for linux_find_cdev() changed to match
> cdevs against inode number ?

These numbers do not come from any user-visible files. They are just 
used internally in the kernel to pass around information.

> cdp_inode is serially generated so on real machine it is really a small
> number for any /dev node.  You can watch that by ls -l /dev.

Sure.

> 

While at it, I found that contrib/mknod/pack_dev.c, still has hardcoded 
references to the old makedev():

> contrib/mknod/pack_dev.c:#define        makedev_freebsd(x,y)    ((portdev_t)((((x) << 8) & 0x0000ff00) | \
> contrib/mknod/pack_dev.c:               dev = makedev_freebsd(numbers[0], numbers[1]);

Same goes for: contrib/libarchive/libarchive/archive_pack_dev.c

And if you "grep -r makedev /usr/src" you'll find more.

--HPS