On (12/04/16 12:55), Greg KH wrote: [..] > That's fine, the issue is that reading a file should not cause the > system state to change. That's just not a logical thing to have happen, > no other sysfs files do that. Why is zram "special" in this way? yeah, zram is not really special, we just didn't come up with anything better than that. > > some history. we started with a 'loop device'-like scheme, but > > ended up with a sysfs approach > > > > [1] https://marc.info/?l=linux-kernel&m=142495984002611 > > [2] https://marc.info/?l=linux-kernel&m=142507747808572 > > [3] https://marc.info/?l=linux-kernel&m=142530591720172 > > [4] https://marc.info/?l=linux-kernel&m=142509446812318 > > [5] https://marc.info/?l=linux-kernel&m=142509782112819 > > you should have stuck with the "write a value to the sysfs file" api, > for some reason that didn't stick... yes, we had this 'echo ID > /sys/..../zram_add' at some point, but it didn't fly. > > I believe we have a documentation > > > > Documentation/ABI/testing/sysfs-class-zram > > and > > Documentation/blockdev/zram.txt > > > > both explain this attr. > > Yes, but that's not in the code itself. You are doing something VERY > different here than any other sysfs file. The code better explain it > very well so that I don't go and change this back sometime in the future > when I sweep the kernel for "odd sysfs mode values" like I do every few > years. > > So comment this please, why would you object to that? oh, I'm not objecting. I just gave as much info as possible. v2 [with a comment] will be out soon. will this comment suffice? ==== diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c index ee03464..3a0576f 100644 --- a/drivers/block/zram/zram_drv.c +++ b/drivers/block/zram/zram_drv.c @@ -1413,6 +1413,13 @@ static ssize_t hot_remove_store(struct class *class, return ret ? ret : count; } +/* + * NOTE: hot_add attribute is not the usual read-only sysfs + * attribute. In a sence that reading from this file does alter + * the state of your system -- it creates a new un-initialized + * zram device and returns back this device's device_id (or an + * error code if it fails to create a new device). + */ static struct class_attribute zram_control_class_attrs[] = { __ATTR(hot_add, 0400, hot_add_show, NULL), __ATTR(hot_remove, 0200, NULL, hot_remove_store), -- -ss -- To unsubscribe from this list: send the line "unsubscribe stable" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html