• Satyam Sharma's avatar
    [NET] netconsole: Support dynamic reconfiguration using configfs · 0bcc1816
    Satyam Sharma authored
    Based upon initial work by Keiichi Kii <k-keiichi@bx.jp.nec.com>.
    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
    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: default avatarSatyam Sharma <satyam@infradead.org>
    Acked-by: default avatarKeiichi Kii <k-keiichi@bx.jp.nec.com>
    Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
    Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
netpoll.h 2.68 KB