quota: send messages via netlink

Implement sending of quota messages via netlink interface.  The advantage
is that in userspace we can better decide what to do with the message - for
example display a dialogue in your X session or just write the message to
the console.  As a bonus, we can get rid of problems with console locking
deep inside filesystem code once we remove the old printing mechanism.

Signed-off-by: Jan Kara <jack@suse.cz>
Cc: Randy Dunlap <randy.dunlap@oracle.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

4 files changed, 222 insertions, 30 deletions

diff --git a/Documentation/filesystems/quota.txt b/Documentation/filesystems/quota.txt
new file mode 100644
index 000000000000..a590c4093eff
--- /dev/null
+++ b/Documentation/filesystems/quota.txt
@@ -0,0 +1,59 @@
+
+Quota subsystem
+===============
+
+Quota subsystem allows system administrator to set limits on used space and
+number of used inodes (inode is a filesystem structure which is associated
+with each file or directory) for users and/or groups. For both used space and
+number of used inodes there are actually two limits. The first one is called
+softlimit and the second one hardlimit.  An user can never exceed a hardlimit
+for any resource. User is allowed to exceed softlimit but only for limited
+period of time. This period is called "grace period" or "grace time". When
+grace time is over, user is not able to allocate more space/inodes until he
+frees enough of them to get below softlimit.
+
+Quota limits (and amount of grace time) are set independently for each
+filesystem.
+
+For more details about quota design, see the documentation in quota-tools package
+(http://sourceforge.net/projects/linuxquota).
+
+Quota netlink interface
+=======================
+When user exceeds a softlimit, runs out of grace time or reaches hardlimit,
+quota subsystem traditionally printed a message to the controlling terminal of
+the process which caused the excess. This method has the disadvantage that
+when user is using a graphical desktop he usually cannot see the message.
+Thus quota netlink interface has been designed to pass information about
+the above events to userspace. There they can be captured by an application
+and processed accordingly.
+
+The interface uses generic netlink framework (see
+http://lwn.net/Articles/208755/ and http://people.suug.ch/~tgr/libnl/ for more
+details about this layer). The name of the quota generic netlink interface
+is "VFS_DQUOT". Definitions of constants below are in <linux/quota.h>.
+  Currently, the interface supports only one message type QUOTA_NL_C_WARNING.
+This command is used to send a notification about any of the above mentioned
+events. Each message has six attributes. These are (type of the argument is
+in parentheses):
+        QUOTA_NL_A_QTYPE (u32)
+          - type of quota being exceeded (one of USRQUOTA, GRPQUOTA)
+        QUOTA_NL_A_EXCESS_ID (u64)
+          - UID/GID (depends on quota type) of user / group whose limit
+            is being exceeded.
+        QUOTA_NL_A_CAUSED_ID (u64)
+          - UID of a user who caused the event
+        QUOTA_NL_A_WARNING (u32)
+          - what kind of limit is exceeded:
+                QUOTA_NL_IHARDWARN - inode hardlimit
+                QUOTA_NL_ISOFTLONGWARN - inode softlimit is exceeded longer
+                  than given grace period
+                QUOTA_NL_ISOFTWARN - inode softlimit
+                QUOTA_NL_BHARDWARN - space (block) hardlimit
+                QUOTA_NL_BSOFTLONGWARN - space (block) softlimit is exceeded
+                  longer than given grace period.
+                QUOTA_NL_BSOFTWARN - space (block) softlimit
+        QUOTA_NL_A_DEV_MAJOR (u32)
+          - major number of a device with the affected filesystem
+        QUOTA_NL_A_DEV_MINOR (u32)
+          - minor number of a device with the affected filesystem
diff --git a/fs/Kconfig b/fs/Kconfig
index f0df9a2e19e1..dc06033f8502 100644
--- a/fs/Kconfig
+++ b/fs/Kconfig
@@ -534,6 +534,24 @@ config QUOTA
           with the quota tools. Probably the quota support is only useful for
           multi user systems. If unsure, say N.
 
+config QUOTA_NETLINK_INTERFACE
+        bool "Report quota messages through netlink interface"
+        depends on QUOTA && NET
+        help
+          If you say Y here, quota warnings (about exceeding softlimit, reaching
+          hardlimit, etc.) will be reported through netlink interface. If unsure,
+          say Y.
+
+config PRINT_QUOTA_WARNING
+        bool "Print quota warnings to console (OBSOLETE)"
+        depends on QUOTA
+        default y
+        help
+          If you say Y here, quota warnings (about exceeding softlimit, reaching
+          hardlimit, etc.) will be printed to the process' controlling terminal.
+          Note that this behavior is currently deprecated and may go away in
+          future. Please use notification via netlink socket instead.
+
 config QFMT_V1
         tristate "Old quota format support"
         depends on QUOTA
diff --git a/fs/dquot.c b/fs/dquot.c
index de9a29f64ff3..2809768d9c41 100644
--- a/fs/dquot.c
+++ b/fs/dquot.c
@@ -79,6 +79,10 @@
 #include <linux/capability.h>
 #include <linux/quotaops.h>
 #include <linux/writeback.h> /* for inode_lock, oddly enough.. */
+#ifdef CONFIG_QUOTA_NETLINK_INTERFACE
+#include <net/netlink.h>
+#include <net/genetlink.h>
+#endif
 
 #include <asm/uaccess.h>
 
@@ -823,6 +827,7 @@ static inline void dquot_decr_space(struct dquot *dquot, qsize_t number)
         clear_bit(DQ_BLKS_B, &dquot->dq_flags);
 }
 
+#ifdef CONFIG_PRINT_QUOTA_WARNING
 static int flag_print_warnings = 1;
 
 static inline int need_print_warning(struct dquot *dquot)
@@ -839,22 +844,15 @@ static inline int need_print_warning(struct dquot *dquot)
         return 0;
 }
 
-/* Values of warnings */
-#define NOWARN 0
-#define IHARDWARN 1
-#define ISOFTLONGWARN 2
-#define ISOFTWARN 3
-#define BHARDWARN 4
-#define BSOFTLONGWARN 5
-#define BSOFTWARN 6
-
 /* Print warning to user which exceeded quota */
 static void print_warning(struct dquot *dquot, const char warntype)
 {
         char *msg = NULL;
         struct tty_struct *tty;
-        int flag = (warntype == BHARDWARN || warntype == BSOFTLONGWARN) ? DQ_BLKS_B :
-          ((warntype == IHARDWARN || warntype == ISOFTLONGWARN) ? DQ_INODES_B : 0);
+        int flag = (warntype == QUOTA_NL_BHARDWARN ||
+                warntype == QUOTA_NL_BSOFTLONGWARN) ? DQ_BLKS_B :
+                ((warntype == QUOTA_NL_IHARDWARN ||
+                warntype == QUOTA_NL_ISOFTLONGWARN) ? DQ_INODES_B : 0);
 
         if (!need_print_warning(dquot) || (flag && test_and_set_bit(flag, &dquot->dq_flags)))
                 return;
@@ -864,28 +862,28 @@ static void print_warning(struct dquot *dquot, const char warntype)
         if (!tty)
                 goto out_lock;
         tty_write_message(tty, dquot->dq_sb->s_id);
-        if (warntype == ISOFTWARN || warntype == BSOFTWARN)
+        if (warntype == QUOTA_NL_ISOFTWARN || warntype == QUOTA_NL_BSOFTWARN)
                 tty_write_message(tty, ": warning, ");
         else
                 tty_write_message(tty, ": write failed, ");
         tty_write_message(tty, quotatypes[dquot->dq_type]);
         switch (warntype) {
-                case IHARDWARN:
+                case QUOTA_NL_IHARDWARN:
                         msg = " file limit reached.\r\n";
                         break;
-                case ISOFTLONGWARN:
+                case QUOTA_NL_ISOFTLONGWARN:
                         msg = " file quota exceeded too long.\r\n";
                         break;
-                case ISOFTWARN:
+                case QUOTA_NL_ISOFTWARN:
                         msg = " file quota exceeded.\r\n";
                         break;
-                case BHARDWARN:
+                case QUOTA_NL_BHARDWARN:
                         msg = " block limit reached.\r\n";
                         break;
-                case BSOFTLONGWARN:
+                case QUOTA_NL_BSOFTLONGWARN:
                         msg = " block quota exceeded too long.\r\n";
                         break;
-                case BSOFTWARN:
+                case QUOTA_NL_BSOFTWARN:
                         msg = " block quota exceeded.\r\n";
                         break;
         }
@@ -893,14 +891,93 @@ static void print_warning(struct dquot *dquot, const char warntype)
 out_lock:
         mutex_unlock(&tty_mutex);
 }
+#endif
+
+#ifdef CONFIG_QUOTA_NETLINK_INTERFACE
+
+/* Size of quota netlink message - actually an upperbound for buffer size */
+#define QUOTA_NL_MSG_SIZE 32
+
+/* 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,
+};
+
+/* Send warning to userspace about user which exceeded quota */
+static void send_warning(const struct dquot *dquot, const char warntype)
+{
+        static atomic_t seq;
+        struct sk_buff *skb;
+        void *msg_head;
+        int ret;
+
+        /* 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(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, 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, 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
 
 static inline void flush_warnings(struct dquot **dquots, char *warntype)
 {
         int i;
 
         for (i = 0; i < MAXQUOTAS; i++)
-                if (dquots[i] != NODQUOT && warntype[i] != NOWARN)
+                if (dquots[i] != NODQUOT && warntype[i] != QUOTA_NL_NOWARN) {
+#ifdef CONFIG_PRINT_QUOTA_WARNING
                         print_warning(dquots[i], warntype[i]);
+#endif
+#ifdef CONFIG_QUOTA_NETLINK_INTERFACE
+                        send_warning(dquots[i], warntype[i]);
+#endif
+                }
 }
 
 static inline char ignore_hardlimit(struct dquot *dquot)
@@ -914,14 +991,14 @@ static inline char ignore_hardlimit(struct dquot *dquot)
 /* needs dq_data_lock */
 static int check_idq(struct dquot *dquot, ulong inodes, char *warntype)
 {
-        *warntype = NOWARN;
+        *warntype = QUOTA_NL_NOWARN;
         if (inodes <= 0 || test_bit(DQ_FAKE_B, &dquot->dq_flags))
                 return QUOTA_OK;
 
         if (dquot->dq_dqb.dqb_ihardlimit &&
            (dquot->dq_dqb.dqb_curinodes + inodes) > dquot->dq_dqb.dqb_ihardlimit &&
             !ignore_hardlimit(dquot)) {
-                *warntype = IHARDWARN;
+                *warntype = QUOTA_NL_IHARDWARN;
                 return NO_QUOTA;
         }
 
@@ -929,14 +1006,14 @@ static int check_idq(struct dquot *dquot, ulong inodes, char *warntype)
            (dquot->dq_dqb.dqb_curinodes + inodes) > dquot->dq_dqb.dqb_isoftlimit &&
             dquot->dq_dqb.dqb_itime && get_seconds() >= dquot->dq_dqb.dqb_itime &&
             !ignore_hardlimit(dquot)) {
-                *warntype = ISOFTLONGWARN;
+                *warntype = QUOTA_NL_ISOFTLONGWARN;
                 return NO_QUOTA;
         }
 
         if (dquot->dq_dqb.dqb_isoftlimit &&
            (dquot->dq_dqb.dqb_curinodes + inodes) > dquot->dq_dqb.dqb_isoftlimit &&
             dquot->dq_dqb.dqb_itime == 0) {
-                *warntype = ISOFTWARN;
+                *warntype = QUOTA_NL_ISOFTWARN;
                 dquot->dq_dqb.dqb_itime = get_seconds() + sb_dqopt(dquot->dq_sb)->info[dquot->dq_type].dqi_igrace;
         }
 
@@ -946,7 +1023,7 @@ static int check_idq(struct dquot *dquot, ulong inodes, char *warntype)
 /* needs dq_data_lock */
 static int check_bdq(struct dquot *dquot, qsize_t space, int prealloc, char *warntype)
 {
-        *warntype = 0;
+        *warntype = QUOTA_NL_NOWARN;
         if (space <= 0 || test_bit(DQ_FAKE_B, &dquot->dq_flags))
                 return QUOTA_OK;
 
@@ -954,7 +1031,7 @@ static int check_bdq(struct dquot *dquot, qsize_t space, int prealloc, char *war
            toqb(dquot->dq_dqb.dqb_curspace + space) > dquot->dq_dqb.dqb_bhardlimit &&
             !ignore_hardlimit(dquot)) {
                 if (!prealloc)
-                        *warntype = BHARDWARN;
+                        *warntype = QUOTA_NL_BHARDWARN;
                 return NO_QUOTA;
         }
 
@@ -963,7 +1040,7 @@ static int check_bdq(struct dquot *dquot, qsize_t space, int prealloc, char *war
             dquot->dq_dqb.dqb_btime && get_seconds() >= dquot->dq_dqb.dqb_btime &&
             !ignore_hardlimit(dquot)) {
                 if (!prealloc)
-                        *warntype = BSOFTLONGWARN;
+                        *warntype = QUOTA_NL_BSOFTLONGWARN;
                 return NO_QUOTA;
         }
 
@@ -971,7 +1048,7 @@ static int check_bdq(struct dquot *dquot, qsize_t space, int prealloc, char *war
            toqb(dquot->dq_dqb.dqb_curspace + space) > dquot->dq_dqb.dqb_bsoftlimit &&
             dquot->dq_dqb.dqb_btime == 0) {
                 if (!prealloc) {
-                        *warntype = BSOFTWARN;
+                        *warntype = QUOTA_NL_BSOFTWARN;
                         dquot->dq_dqb.dqb_btime = get_seconds() + sb_dqopt(dquot->dq_sb)->info[dquot->dq_type].dqi_bgrace;
                 }
                 else
@@ -1066,7 +1143,7 @@ out_add:
                 return QUOTA_OK;
         }
         for (cnt = 0; cnt < MAXQUOTAS; cnt++)
-                warntype[cnt] = NOWARN;
+                warntype[cnt] = QUOTA_NL_NOWARN;
 
         down_read(&sb_dqopt(inode->i_sb)->dqptr_sem);
         if (IS_NOQUOTA(inode)) {        /* Now we can do reliable test... */
@@ -1112,7 +1189,7 @@ int dquot_alloc_inode(const struct inode *inode, unsigned long number)
         if (IS_NOQUOTA(inode))
                 return QUOTA_OK;
         for (cnt = 0; cnt < MAXQUOTAS; cnt++)
-                warntype[cnt] = NOWARN;
+                warntype[cnt] = QUOTA_NL_NOWARN;
         down_read(&sb_dqopt(inode->i_sb)->dqptr_sem);
         if (IS_NOQUOTA(inode)) {
                 up_read(&sb_dqopt(inode->i_sb)->dqptr_sem);
@@ -1234,7 +1311,7 @@ int dquot_transfer(struct inode *inode, struct iattr *iattr)
         /* Clear the arrays */
         for (cnt = 0; cnt < MAXQUOTAS; cnt++) {
                 transfer_to[cnt] = transfer_from[cnt] = NODQUOT;
-                warntype[cnt] = NOWARN;
+                warntype[cnt] = QUOTA_NL_NOWARN;
         }
         down_write(&sb_dqopt(inode->i_sb)->dqptr_sem);
         /* Now recheck reliably when holding dqptr_sem */
@@ -1808,6 +1885,7 @@ static ctl_table fs_dqstats_table[] = {
                 .mode           = 0444,
                 .proc_handler   = &proc_dointvec,
         },
+#ifdef CONFIG_PRINT_QUOTA_WARNING
         {
                 .ctl_name       = FS_DQ_WARNINGS,
                 .procname       = "warnings",
@@ -1816,6 +1894,7 @@ static ctl_table fs_dqstats_table[] = {
                 .mode           = 0644,
                 .proc_handler   = &proc_dointvec,
         },
+#endif
         { .ctl_name = 0 },
 };
 
@@ -1877,6 +1956,11 @@ static int __init dquot_init(void)
 
         register_shrinker(&dqcache_shrinker);
 
+#ifdef CONFIG_QUOTA_NETLINK_INTERFACE
+        if (genl_register_family(&quota_genl_family) != 0)
+                printk(KERN_ERR "VFS: Failed to create quota netlink interface.\n");
+#endif
+
         return 0;
 }
 module_init(dquot_init);
diff --git a/include/linux/quota.h b/include/linux/quota.h
index 62439828395e..6e0393a5b2ea 100644
--- a/include/linux/quota.h
+++ b/include/linux/quota.h
@@ -128,6 +128,37 @@ struct if_dqinfo {
         __u32 dqi_valid;
 };
 
+/*
+ * Definitions for quota netlink interface
+ */
+#define QUOTA_NL_NOWARN 0
+#define QUOTA_NL_IHARDWARN 1            /* Inode hardlimit reached */
+#define QUOTA_NL_ISOFTLONGWARN 2        /* Inode grace time expired */
+#define QUOTA_NL_ISOFTWARN 3            /* Inode softlimit reached */
+#define QUOTA_NL_BHARDWARN 4            /* Block hardlimit reached */
+#define QUOTA_NL_BSOFTLONGWARN 5        /* Block grace time expired */
+#define QUOTA_NL_BSOFTWARN 6            /* Block softlimit reached */
+
+enum {
+        QUOTA_NL_C_UNSPEC,
+        QUOTA_NL_C_WARNING,
+        __QUOTA_NL_C_MAX,
+};
+#define QUOTA_NL_C_MAX (__QUOTA_NL_C_MAX - 1)
+
+enum {
+        QUOTA_NL_A_UNSPEC,
+        QUOTA_NL_A_QTYPE,
+        QUOTA_NL_A_EXCESS_ID,
+        QUOTA_NL_A_WARNING,
+        QUOTA_NL_A_DEV_MAJOR,
+        QUOTA_NL_A_DEV_MINOR,
+        QUOTA_NL_A_CAUSED_ID,
+        __QUOTA_NL_A_MAX,
+};
+#define QUOTA_NL_A_MAX (__QUOTA_NL_A_MAX - 1)
+
+
 #ifdef __KERNEL__
 #include <linux/spinlock.h>
 #include <linux/rwsem.h>