netlink.c

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#include <linux/cred.h>
#include <linux/init.h>
#include <linux/module.h>
#include <linux/kernel.h>
#include <linux/quotaops.h>
#include <linux/sched.h>
#include <linux/slab.h>
#include <net/netlink.h>
#include <net/genetlink.h>

/* Netlink family structure for quota */
static struct genl_family quota_genl_family = {
    .id = GENL_ID_GENERATE,
    .hdrsize = 0,
    .name = "VFS_DQUOT",
    .version = 1,
    .maxattr = QUOTA_NL_A_MAX,
};

void quota_send_warning(struct kqid qid, dev_t dev,
            const char warntype)
{
    static atomic_t seq;
    struct sk_buff *skb;
    void *msg_head;
    int ret;
    int msg_size = 4 * nla_total_size(sizeof(u32)) +
               2 * nla_total_size(sizeof(u64));

    /* We have to allocate using GFP_NOFS as we are called from a
     * filesystem performing write and thus further recursion into
     * the fs to free some data could cause deadlocks. */
    skb = genlmsg_new(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, atomic_add_return(1, &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, qid.type);
    if (ret)
        goto attr_err_out;
    ret = nla_put_u64(skb, QUOTA_NL_A_EXCESS_ID,
              from_kqid_munged(&init_user_ns, qid));
    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(dev));
    if (ret)
        goto attr_err_out;
    ret = nla_put_u32(skb, QUOTA_NL_A_DEV_MINOR, MINOR(dev));
    if (ret)
        goto attr_err_out;
    ret = nla_put_u64(skb, QUOTA_NL_A_CAUSED_ID,
              from_kuid_munged(&init_user_ns, current_uid()));
    if (ret)
        goto attr_err_out;
    genlmsg_end(skb, msg_head);

    genlmsg_multicast(skb, 0, quota_genl_family.id, GFP_NOFS);
    return;
attr_err_out:
    printk(KERN_ERR "VFS: Not enough space to compose quota message!\n");
err_out:
    kfree_skb(skb);
}
EXPORT_SYMBOL(quota_send_warning);

static int __init quota_init(void)
{
    if (genl_register_family(&quota_genl_family) != 0)
        printk(KERN_ERR
               "VFS: Failed to create quota netlink interface.\n");
    return 0;
};

module_init(quota_init);