From 0bcc1816188e570bde1d56a208996660f2633ae0 Mon Sep 17 00:00:00 2001 From: Satyam Sharma Date: Fri, 10 Aug 2007 15:35:05 -0700 Subject: [NET] netconsole: Support dynamic reconfiguration using configfs Based upon initial work by Keiichi Kii . This patch introduces support for dynamic reconfiguration (adding, removing and/or modifying parameters of netconsole targets at runtime) using a userspace interface exported via configfs. Documentation is also updated accordingly. Issues and brief design overview: (1) Kernel-initiated creation / destruction of kernel objects is not possible with configfs -- the lifetimes of the "config items" is managed exclusively from userspace. But netconsole must support boot/module params too, and these are parsed in kernel and hence netpolls must be setup from the kernel. Joel Becker suggested to separately manage the lifetimes of the two kinds of netconsole_target objects -- those created via configfs mkdir(2) from userspace and those specified from the boot/module option string. This adds complexity and some redundancy here and also means that boot/module param-created targets are not exposed through the configfs namespace (and hence cannot be updated / destroyed dynamically). However, this saves us from locking / refcounting complexities that would need to be introduced in configfs to support kernel-initiated item creation / destroy there. (2) In configfs, item creation takes place in the call chain of the mkdir(2) syscall in the driver subsystem. If we used an ioctl(2) to create / destroy objects from userspace, the special userspace program is able to fill out the structure to be passed into the ioctl and hence specify attributes such as local interface that are required at the time we set up the netpoll. For configfs, this information is not available at the time of mkdir(2). So, we keep all newly-created targets (via configfs) disabled by default. The user is expected to set various attributes appropriately (including the local network interface if required) and then write(2) "1" to the "enabled" attribute. Thus, netpoll_setup() is then called on the set parameters in the context of _this_ write(2) on the "enabled" attribute itself. This design enables the user to reconfigure existing netconsole targets at runtime to be attached to newly-come-up interfaces that may not have existed when netconsole was loaded or when the targets were actually created. All this effectively enables us to get rid of custom ioctls. (3) Ultra-paranoid configfs attribute show() and store() operations, with sanity and input range checking, using only safe string primitives, and compliant with the recommendations in Documentation/filesystems/sysfs.txt. (4) A new function netpoll_print_options() is created in the netpoll API, that just prints out the configured parameters for a netpoll structure. netpoll_parse_options() is modified to use that and it is also exported to be used from netconsole. Signed-off-by: Satyam Sharma Acked-by: Keiichi Kii Signed-off-by: Andrew Morton Signed-off-by: David S. Miller --- include/linux/netpoll.h | 1 + 1 file changed, 1 insertion(+) (limited to 'include/linux/netpoll.h') diff --git a/include/linux/netpoll.h b/include/linux/netpoll.h index 08dcc39ec18d..20250d963d72 100644 --- a/include/linux/netpoll.h +++ b/include/linux/netpoll.h @@ -35,6 +35,7 @@ struct netpoll_info { void netpoll_poll(struct netpoll *np); void netpoll_send_udp(struct netpoll *np, const char *msg, int len); +void netpoll_print_options(struct netpoll *np); int netpoll_parse_options(struct netpoll *np, char *opt); int netpoll_setup(struct netpoll *np); int netpoll_trap(void); -- cgit v1.2.3-58-ga151