On Tue, 28 Aug 2007 16:13:18 +0200 Jan Kara <[EMAIL PROTECTED]> wrote:
> Hello,
>
> I'm sending rediffed patch implementing sending of quota messages via
> netlink
> interface (some rationale in patch description). I've already posted it to
> LKML some time ago and there were no objections, so I guess it's fine to put
> it to -mm. Andrew, would you be so kind? Thanks.
> Userspace deamon reading the messages from the kernel and sending them to
> dbus and/or user console is also written (it's part of quota-tools). The
> only remaining problem is there are a few changes needed to libnl needed for
> the userspace daemon. They were basically acked by the maintainer but it
> seems he has not merged the patches yet. So this will take a bit more time.
>
So it's a new kernel->userspace interface.
But we have no description of the interface :(
> +/* Send warning to userspace about user which exceeded quota */
> +static void send_warning(const struct dquot *dquot, const char warntype)
> +{
> + static unsigned long seq;
> + struct sk_buff *skb;
> + void *msg_head;
> + int ret;
> +
> + skb = genlmsg_new(QUOTA_NL_MSG_SIZE, GFP_NOFS);
> + if (!skb) {
> + printk(KERN_ERR
> + "VFS: Not enough memory to send quota warning.\n");
> + return;
> + }
> + msg_head = genlmsg_put(skb, 0, seq++, "a_genl_family, 0,
> QUOTA_NL_C_WARNING);
> + if (!msg_head) {
> + printk(KERN_ERR
> + "VFS: Cannot store netlink header in quota warning.\n");
> + goto err_out;
> + }
> + ret = nla_put_u32(skb, QUOTA_NL_A_QTYPE, dquot->dq_type);
> + if (ret)
> + goto attr_err_out;
> + ret = nla_put_u64(skb, QUOTA_NL_A_EXCESS_ID, dquot->dq_id);
> + if (ret)
> + goto attr_err_out;
> + ret = nla_put_u32(skb, QUOTA_NL_A_WARNING, warntype);
> + if (ret)
> + goto attr_err_out;
> + ret = nla_put_u32(skb, QUOTA_NL_A_DEV_MAJOR,
> + MAJOR(dquot->dq_sb->s_dev));
> + if (ret)
> + goto attr_err_out;
> + ret = nla_put_u32(skb, QUOTA_NL_A_DEV_MINOR,
> + MINOR(dquot->dq_sb->s_dev));
> + if (ret)
> + goto attr_err_out;
> + ret = nla_put_u64(skb, QUOTA_NL_A_CAUSED_ID, current->user->uid);
> + if (ret)
> + goto attr_err_out;
> + genlmsg_end(skb, msg_head);
> +
> + ret = genlmsg_multicast(skb, 0, quota_genl_family.id, GFP_NOFS);
> + if (ret < 0 && ret != -ESRCH)
> + printk(KERN_ERR
> + "VFS: Failed to send notification message: %d\n", ret);
> + return;
> +attr_err_out:
> + printk(KERN_ERR "VFS: Failed to compose quota message: %d\n", ret);
> +err_out:
> + kfree_skb(skb);
> +}
> +#endif
This is it. Normally netlink payloads are represented as a struct. How
come this one is built-by-hand?
It doesn't appear to be versioned. Should it be?
Does it have (or need) reserved-set-to-zero space for expansion? Again,
hard to tell..
I guess it's OK to send a major and minor out of the kernel like this.
What's it for? To represent a filesytem? I wonder if there's a more
modern and useful way of describing the fs. Path to mountpoint or
something?
I suspect the namespace virtualisation guys would be interested in a new
interface which is sending current->user->uid up to userspace. uids are
per-namespace now. What are the implications? (cc's added)
Is it worth adding a comment explaining why GFP_NOFS is used here?
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