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    SubjectRe: [PATCH] Send quota messages via netlink
    Date
    Andrew Morton <akpm@linux-foundation.org> writes:

    > On Tue, 28 Aug 2007 16:13:18 +0200 Jan Kara <jack@suse.cz> 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++, &quota_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?

    No netlink fields (unless I'm confused) are represented as a struct,
    not the entire netlink payload.

    > It doesn't appear to be versioned. Should it be?

    Well. If it is using netlink properly each field should have a tag.
    So it should not need to be versioned, because each field is strictly
    controlled.

    > Does it have (or need) reserved-set-to-zero space for expansion? Again,
    > hard to tell..

    Not if netlink is used properly. Just another nested tag.

    > 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?

    Or perhaps the string the fs was mounted with.

    > 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)

    That we definitely would be. Although the user namespaces is rather
    strongly incomplete at the moment.

    > Is it worth adding a comment explaining why GFP_NOFS is used here?
    -
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