Messages in this thread Patch in this message | | | Subject | Re: add devname module aliases to allow module on-demand auto-loading | From | Kay Sievers <> | Date | Fri, 21 May 2010 13:24:13 +0200 |
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On Fri, 2010-05-21 at 19:11 +0800, Ian Kent wrote: > On Thu, 2010-05-20 at 18:07 +0200, Kay Sievers wrote:
> > --- a/fs/autofs4/dev-ioctl.c > > +MODULE_ALIAS_MISCDEV(BTRFS_MINOR); > > Is this a typo or am I missing something?
Yikes, sorry, that's just broken. New patch. Thanks a lot for checking.
Kay
From: Kay Sievers <kay.sievers@vrfy.org> Subject: add devname module aliases to allow module on-demand auto-loading
This adds: alias: devname:<name> to some common kernel modules, which will allow the on-demand loading of the kernel module when the device node is accessed.
Ideally all these modules would be compiled-in, but distros seems too much in love with their modularization that we need to cover the common cases with this new facility. It will allow us to remove a bunch of pretty useless init scripts and modprobes from init scripts.
The static device node aliases will be carried in the module itself. The program depmod will extract this information to a file in the module directory: $ cat /lib/modules/2.6.34-00650-g537b60d-dirty/modules.devname # Device nodes to trigger on-demand module loading. microcode cpu/microcode c10:184 fuse fuse c10:229 ppp_generic ppp c108:0 tun net/tun c10:200 dm_mod mapper/control c10:235
Udev will pick up the depmod created file on startup and create all the static device nodes which the kernel modules specify, so that these modules get automatically loaded when the device node is accessed: $ /sbin/udevd --debug ... static_dev_create_from_modules: mknod '/dev/cpu/microcode' c10:184 static_dev_create_from_modules: mknod '/dev/fuse' c10:229 static_dev_create_from_modules: mknod '/dev/ppp' c108:0 static_dev_create_from_modules: mknod '/dev/net/tun' c10:200 static_dev_create_from_modules: mknod '/dev/mapper/control' c10:235 udev_rules_apply_static_dev_perms: chmod '/dev/net/tun' 0666 udev_rules_apply_static_dev_perms: chmod '/dev/fuse' 0666
A few device nodes are switched to statically allocated numbers, to allow the static nodes to work. This might also useful for systems which still run a plain static /dev, which is completely unsafe to use with any dynamic minor numbers.
Note: The devname aliases must be limited to the *common* and *single*instance* device nodes, like the misc devices, and never be used for conceptually limited systems like the loop devices, which should rather get fixed properly and get a control node for losetup to talk to, instead of creating a random number of device nodes in advance, regardless if they are ever used.
This facility is to hide the mess distros are creating with too modualized kernels, and just to hide that these modules are not compiled-in, and not to paper-over broken concepts. Thanks! :)
Cc: Greg Kroah-Hartman <gregkh@suse.de> Cc: David S. Miller <davem@davemloft.net> Cc: Miklos Szeredi <miklos@szeredi.hu> Cc: Chris Mason <chris.mason@oracle.com> Cc: Alasdair G Kergon <agk@redhat.com> Cc: Tigran Aivazian <tigran@aivazian.fsnet.co.uk> Cc: Ian Kent <raven@themaw.net> Signed-Off-By: Kay Sievers <kay.sievers@vrfy.org> ---
Documentation/devices.txt | 3 +++ arch/x86/kernel/microcode_core.c | 1 + drivers/md/dm-ioctl.c | 5 ++++- drivers/net/ppp_generic.c | 4 ++-- drivers/net/tun.c | 1 + fs/autofs4/dev-ioctl.c | 5 ++++- fs/btrfs/super.c | 5 ++++- fs/fuse/dev.c | 1 + include/linux/miscdevice.h | 3 +++ 9 files changed, 23 insertions(+), 5 deletions(-)
--- a/Documentation/devices.txt +++ b/Documentation/devices.txt @@ -443,6 +443,9 @@ Your cooperation is appreciated. 231 = /dev/snapshot System memory snapshot device 232 = /dev/kvm Kernel-based virtual machine (hardware virtualization extensions) 233 = /dev/kmview View-OS A process with a view + 234 = /dev/btrfs-control Btrfs control device + 235 = /dev/mapper/control Device-Mapper control device + 236 = /dev/autofs Autofs control device 240-254 Reserved for local use 255 Reserved for MISC_DYNAMIC_MINOR --- a/arch/x86/kernel/microcode_core.c +++ b/arch/x86/kernel/microcode_core.c @@ -260,6 +260,7 @@ static void microcode_dev_exit(void) } MODULE_ALIAS_MISCDEV(MICROCODE_MINOR); +MODULE_ALIAS("devname:cpu/microcode"); #else #define microcode_dev_init() 0 #define microcode_dev_exit() do { } while (0) --- a/drivers/md/dm-ioctl.c +++ b/drivers/md/dm-ioctl.c @@ -1599,12 +1599,15 @@ static const struct file_operations _ctl }; static struct miscdevice _dm_misc = { - .minor = MISC_DYNAMIC_MINOR, + .minor = MAPPER_CTRL_MINOR, .name = DM_NAME, .nodename = "mapper/control", .fops = &_ctl_fops }; +MODULE_ALIAS_MISCDEV(MAPPER_CTRL_MINOR); +MODULE_ALIAS("devname:mapper/control"); + /* * Create misc character device and link to DM_DIR/control. */ --- a/drivers/net/ppp_generic.c +++ b/drivers/net/ppp_generic.c @@ -2907,5 +2907,5 @@ EXPORT_SYMBOL(ppp_output_wakeup); EXPORT_SYMBOL(ppp_register_compressor); EXPORT_SYMBOL(ppp_unregister_compressor); MODULE_LICENSE("GPL"); -MODULE_ALIAS_CHARDEV_MAJOR(PPP_MAJOR); -MODULE_ALIAS("/dev/ppp"); +MODULE_ALIAS_CHARDEV(PPP_MAJOR, 0); +MODULE_ALIAS("devname:ppp"); --- a/drivers/net/tun.c +++ b/drivers/net/tun.c @@ -1624,3 +1624,4 @@ MODULE_DESCRIPTION(DRV_DESCRIPTION); MODULE_AUTHOR(DRV_COPYRIGHT); MODULE_LICENSE("GPL"); MODULE_ALIAS_MISCDEV(TUN_MINOR); +MODULE_ALIAS("devname:net/tun"); --- a/fs/autofs4/dev-ioctl.c +++ b/fs/autofs4/dev-ioctl.c @@ -736,11 +736,14 @@ static const struct file_operations _dev }; static struct miscdevice _autofs_dev_ioctl_misc = { - .minor = MISC_DYNAMIC_MINOR, + .minor = AUTOFS_MINOR, .name = AUTOFS_DEVICE_NAME, .fops = &_dev_ioctl_fops }; +MODULE_ALIAS_MISCDEV(AUTOFS_MINOR); +MODULE_ALIAS("devname:autofs"); + /* Register/deregister misc character device */ int autofs_dev_ioctl_init(void) { --- a/fs/btrfs/super.c +++ b/fs/btrfs/super.c @@ -832,11 +832,14 @@ static const struct file_operations btrf }; static struct miscdevice btrfs_misc = { - .minor = MISC_DYNAMIC_MINOR, + .minor = BTRFS_MINOR, .name = "btrfs-control", .fops = &btrfs_ctl_fops }; +MODULE_ALIAS_MISCDEV(BTRFS_MINOR); +MODULE_ALIAS("devname:btrfs-control"); + static int btrfs_interface_init(void) { return misc_register(&btrfs_misc); --- a/fs/fuse/dev.c +++ b/fs/fuse/dev.c @@ -18,6 +18,7 @@ #include <linux/slab.h> MODULE_ALIAS_MISCDEV(FUSE_MINOR); +MODULE_ALIAS("devname:fuse"); static struct kmem_cache *fuse_req_cachep; --- a/include/linux/miscdevice.h +++ b/include/linux/miscdevice.h @@ -31,6 +31,9 @@ #define FUSE_MINOR 229 #define KVM_MINOR 232 #define VHOST_NET_MINOR 233 +#define BTRFS_MINOR 234 +#define MAPPER_CTRL_MINOR 235 +#define AUTOFS_MINOR 236 #define MISC_DYNAMIC_MINOR 255 struct device;
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