Re: [PATCH 2/2] chardev: showing minor range for chardev in the output of /proc/devices

From: cgxu519
Date: Tue Feb 12 2019 - 10:41:52 EST

On 2/12/19 11:20 PM, Greg KH wrote:
On Tue, Feb 12, 2019 at 11:18:22PM +0800, cgxu519 wrote:
On 2/12/19 5:02 PM, Greg KH wrote:
On Tue, Feb 12, 2019 at 04:47:39PM +0800, Chengguang Xu wrote:
Currently chardev allows to share major, showing
major with minor range for chardev will be more

Signed-off-by: Chengguang Xu <cgxu519@xxxxxxx>
fs/char_dev.c | 4 +++-
1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/fs/char_dev.c b/fs/char_dev.c
index b25b1da097d5..6f00acdeb308 100644
--- a/fs/char_dev.c
+++ b/fs/char_dev.c
@@ -55,7 +55,9 @@ void chrdev_show(struct seq_file *f, off_t offset)
for (cd = chrdevs[major_to_index(offset)]; cd; cd = cd->next) {
if (cd->major == offset)
- seq_printf(f, "%3d %s\n", cd->major, cd->name);
+ seq_printf(f, "%3d %s (%u-%u)\n", cd->major, cd->name,
+ cd->baseminor,
+ cd->baseminor + cd->minorct - 1);
You are changing the format of a userspace file, what tools are going to
break when you do this?
I'll remove this part in V2. Do you have any idea how to get the minor
range info for particular major? Or adding a similar file to somewhere
under /sys is acceptable?
Why do you need to know the minor range? What can userspace do with
this that actually matters?

Assume that when we try to load a driver module and fail with -EBUSY
because of minor range overlapping, then what can we do for this case?
we even don't know what range has occupied and what range is available.

Also, I think we can obviously notice range overlapping bugs by showing
all registered minor ranges.