sysfs: add /sys/dev/{char,block} to lookup sysfs path by major:minor From: Dan Williams Why?: There are occasions where userspace would like to access sysfs attributes for a device but it may not know how sysfs has named the device or the path. For example what is the sysfs path for /dev/disk/by-id/ata-ST3160827AS_5MT004CK? With this change a call to stat(2) returns the major:minor then userspace can see that /sys/dev/block/8:32 links to /sys/block/sdc. What are the alternatives?: 1/ Add an ioctl to return the path: Doable, but sysfs is meant to reduce the need to proliferate ioctl interfaces into the kernel, so this seems counter productive. 2/ Use udev to create these symlinks: Also doable, but it adds a udev dependency to utilities that might be running in a limited environment like an initramfs. Cc: NeilBrown Cc: Tejun Heo Cc: Kay Sievers Cc: Greg KH Cc: Mark Lord Cc: H. Peter Anvin Signed-off-by: Dan Williams --- drivers/base/core.c | 37 ++++++++++++++++++++++++++++++++++++- 1 files changed, 36 insertions(+), 1 deletions(-) diff --git a/drivers/base/core.c b/drivers/base/core.c index 24198ad..de925f8 100644 --- a/drivers/base/core.c +++ b/drivers/base/core.c @@ -27,6 +27,9 @@ int (*platform_notify)(struct device *dev) = NULL; int (*platform_notify_remove)(struct device *dev) = NULL; +static struct kobject *dev_kobj; +static struct kobject *char_kobj; +static struct kobject *block_kobj; #ifdef CONFIG_BLOCK static inline int device_is_not_partition(struct device *dev) @@ -759,6 +762,11 @@ static void device_remove_class_symlinks(struct device *dev) sysfs_remove_link(&dev->kobj, "subsystem"); } +static struct kobject *device_to_dev_kobj(struct device *dev) +{ + return dev->class == &block_class ? block_kobj : char_kobj; +} + /** * device_add - add device to device hierarchy. * @dev: device. @@ -775,6 +783,7 @@ int device_add(struct device *dev) struct device *parent = NULL; struct class_interface *class_intf; int error; + char devt_str[25]; dev = get_device(dev); if (!dev || !strlen(dev->bus_id)) { @@ -806,9 +815,16 @@ int device_add(struct device *dev) goto attrError; if (MAJOR(dev->devt)) { + struct kobject *kobj = device_to_dev_kobj(dev); + error = device_create_file(dev, &devt_attr); if (error) goto ueventattrError; + + format_dev_t(devt_str, dev->devt); + error = sysfs_create_link(kobj, &dev->kobj, devt_str); + if (error) + goto devtattrError; } error = device_add_class_symlinks(dev); @@ -854,6 +870,9 @@ int device_add(struct device *dev) device_remove_class_symlinks(dev); SymlinkError: if (MAJOR(dev->devt)) + sysfs_remove_link(device_to_dev_kobj(dev), devt_str); + devtattrError: + if (MAJOR(dev->devt)) device_remove_file(dev, &devt_attr); ueventattrError: device_remove_file(dev, &uevent_attr); @@ -925,12 +944,16 @@ void device_del(struct device *dev) { struct device *parent = dev->parent; struct class_interface *class_intf; + char devt_str[25]; device_pm_remove(dev); if (parent) klist_del(&dev->knode_parent); - if (MAJOR(dev->devt)) + if (MAJOR(dev->devt)) { + format_dev_t(devt_str, dev->devt); + sysfs_remove_link(device_to_dev_kobj(dev), devt_str); device_remove_file(dev, &devt_attr); + } if (dev->class) { device_remove_class_symlinks(dev); @@ -1055,6 +1078,15 @@ int __init devices_init(void) devices_kset = kset_create_and_add("devices", &device_uevent_ops, NULL); if (!devices_kset) return -ENOMEM; + dev_kobj = kobject_create_and_add("dev", NULL); + if (!dev_kobj) + return -ENOMEM; + block_kobj = kobject_create_and_add("block", dev_kobj); + if (!block_kobj) + return -ENOMEM; + char_kobj = kobject_create_and_add("char", dev_kobj); + if (!char_kobj) + return -ENOMEM; return 0; } @@ -1380,4 +1412,7 @@ void device_shutdown(void) dev->driver->shutdown(dev); } } + kobject_put(char_kobj); + kobject_put(block_kobj); + kobject_put(dev_kobj); }