@@ -10,6 +10,8 @@ opened by userspace. This can be used in conjunction with::
* Mount notifications.
+ * Superblock notifications.
+
The notifications buffers can be enabled by:
"General setup"/"General notification queue"
@@ -239,6 +241,12 @@ Any particular buffer can be fed from multiple sources. Sources include:
Notifications of this type indicate changes to mount attributes and the
mount topology within the subtree at the indicated point.
+ * WATCH_TYPE_SB_NOTIFY
+
+ Notifications of this type indicate changes to superblock attributes and
+ configuration and events generated within a superblock such as I/O errors,
+ network status changes and out-of-space/out-of-quota errors.
+
Event Filtering
===============
@@ -302,6 +310,7 @@ It can then be set to receive notifications::
keyctl(KEYCTL_WATCH_KEY, KEY_SPEC_SESSION_KEYRING, fds[1], 0x01);
watch_mount(AT_FDCWD, "/", 0, fds[1], 0x02);
+ watch_sb(AT_FDCWD, "/", 0, fds[1], 0x03);
The notifications can then be consumed by something like the following::
@@ -341,6 +350,9 @@ The notifications can then be consumed by something like the following::
case WATCH_TYPE_MOUNT_NOTIFY:
saw_mount_change(&n.n);
break;
+ case WATCH_TYPE_SB_NOTIFY:
+ saw_sb_event(&n.n);
+ break;
}
p += len;
@@ -478,3 +478,4 @@
547 common openat2 sys_openat2
548 common pidfd_getfd sys_pidfd_getfd
549 common watch_mount sys_watch_mount
+550 common watch_sb sys_watch_sb
@@ -452,3 +452,4 @@
437 common openat2 sys_openat2
438 common pidfd_getfd sys_pidfd_getfd
439 common watch_mount sys_watch_mount
+440 common watch_sb sys_watch_sb
@@ -38,7 +38,7 @@
#define __ARM_NR_compat_set_tls (__ARM_NR_COMPAT_BASE + 5)
#define __ARM_NR_COMPAT_END (__ARM_NR_COMPAT_BASE + 0x800)
-#define __NR_compat_syscalls 440
+#define __NR_compat_syscalls 441
#endif
#define __ARCH_WANT_SYS_CLONE
@@ -885,6 +885,8 @@ __SYSCALL(__NR_openat2, sys_openat2)
__SYSCALL(__NR_pidfd_getfd, sys_pidfd_getfd)
#define __NR_watch_mount 439
__SYSCALL(__NR_watch_mount, sys_watch_mount)
+#define __NR_watch_sb 440
+__SYSCALL(__NR_watch_sb, sys_watch_sb)
/*
* Please add new compat syscalls above this comment and update
@@ -359,3 +359,4 @@
437 common openat2 sys_openat2
438 common pidfd_getfd sys_pidfd_getfd
439 common watch_mount sys_watch_mount
+440 common watch_sb sys_watch_sb
@@ -438,3 +438,4 @@
437 common openat2 sys_openat2
438 common pidfd_getfd sys_pidfd_getfd
439 common watch_mount sys_watch_mount
+440 common watch_sb sys_watch_sb
@@ -444,3 +444,4 @@
437 common openat2 sys_openat2
438 common pidfd_getfd sys_pidfd_getfd
439 common watch_mount sys_watch_mount
+440 common watch_sb sys_watch_sb
@@ -377,3 +377,4 @@
437 n32 openat2 sys_openat2
438 n32 pidfd_getfd sys_pidfd_getfd
439 n32 watch_mount sys_watch_mount
+440 n32 watch_sb sys_watch_sb
@@ -353,3 +353,4 @@
437 n64 openat2 sys_openat2
438 n64 pidfd_getfd sys_pidfd_getfd
439 n64 watch_mount sys_watch_mount
+440 n64 watch_sb sys_watch_sb
@@ -426,3 +426,4 @@
437 o32 openat2 sys_openat2
438 o32 pidfd_getfd sys_pidfd_getfd
439 o32 watch_mount sys_watch_mount
+440 o32 watch_sb sys_watch_sb
@@ -436,3 +436,4 @@
437 common openat2 sys_openat2
438 common pidfd_getfd sys_pidfd_getfd
439 common watch_mount sys_watch_mount
+440 common watch_sb sys_watch_sb
@@ -520,3 +520,4 @@
437 common openat2 sys_openat2
438 common pidfd_getfd sys_pidfd_getfd
439 common watch_mount sys_watch_mount
+440 common watch_sb sys_watch_sb
@@ -441,3 +441,4 @@
437 common openat2 sys_openat2 sys_openat2
438 common pidfd_getfd sys_pidfd_getfd sys_pidfd_getfd
439 common watch_mount sys_watch_mount sys_watch_mount
+440 common watch_sb sys_watch_sb sys_watch_sb
@@ -441,3 +441,4 @@
437 common openat2 sys_openat2
438 common pidfd_getfd sys_pidfd_getfd
439 common watch_mount sys_watch_mount
+440 common watch_sb sys_watch_sb
@@ -484,3 +484,4 @@
437 common openat2 sys_openat2
438 common pidfd_getfd sys_pidfd_getfd
439 common watch_mount sys_watch_mount
+440 common watch_sb sys_watch_sb
@@ -443,3 +443,4 @@
437 i386 openat2 sys_openat2 __ia32_sys_openat2
438 i386 pidfd_getfd sys_pidfd_getfd __ia32_sys_pidfd_getfd
439 i386 watch_mount sys_watch_mount __ia32_sys_watch_mount
+440 i386 watch_sb sys_watch_sb __ia32_sys_watch_sb
@@ -360,6 +360,7 @@
437 common openat2 __x64_sys_openat2
438 common pidfd_getfd __x64_sys_pidfd_getfd
439 common watch_mount __x64_sys_watch_mount
+440 common watch_sb __x64_sys_watch_sb
#
# x32-specific system call numbers start at 512 to avoid cache impact
@@ -409,3 +409,4 @@
437 common openat2 sys_openat2
438 common pidfd_getfd sys_pidfd_getfd
439 common watch_mount sys_watch_mount
+440 common watch_sb sys_watch_sb
@@ -126,6 +126,18 @@ config MOUNT_NOTIFICATIONS
device to handle the notification buffer and provides the
mount_notify() system call to enable/disable watchpoints.
+config SB_NOTIFICATIONS
+ bool "Superblock event notifications"
+ select WATCH_QUEUE
+ help
+ This option provides support for receiving superblock event
+ notifications. This makes use of the /dev/watch_queue misc device to
+ handle the notification buffer and provides the sb_notify() system
+ call to enable/disable watches.
+
+ Events can include things like changing between R/W and R/O, EIO
+ generation, ENOSPC generation and EDQUOT generation.
+
source "fs/quota/Kconfig"
source "fs/autofs/Kconfig"
@@ -37,6 +37,8 @@
#include <linux/lockdep.h>
#include <linux/user_namespace.h>
#include <linux/fs_context.h>
+#include <linux/syscalls.h>
+#include <linux/namei.h>
#include <uapi/linux/mount.h>
#include "internal.h"
@@ -333,6 +335,10 @@ void deactivate_locked_super(struct super_block *s)
{
struct file_system_type *fs = s->s_type;
if (atomic_dec_and_test(&s->s_active)) {
+#ifdef CONFIG_SB_NOTIFICATIONS
+ if (s->s_watchers)
+ remove_watch_list(s->s_watchers, s->s_unique_id);
+#endif
cleancache_invalidate_fs(s);
unregister_shrinker(&s->s_shrink);
fs->kill_sb(s);
@@ -972,6 +978,8 @@ int reconfigure_super(struct fs_context *fc)
/* Needs to be ordered wrt mnt_is_readonly() */
smp_wmb();
sb->s_readonly_remount = 0;
+ notify_sb(sb, NOTIFY_SUPERBLOCK_READONLY,
+ remount_ro ? NOTIFY_SUPERBLOCK_IS_NOW_RO : 0);
/*
* Some filesystems modify their metadata via some other path than the
@@ -1891,3 +1899,176 @@ void vfs_generate_unique_id(u64 *_id)
*_id = id;
}
+
+#ifdef CONFIG_SB_NOTIFICATIONS
+/*
+ * Post superblock notifications.
+ */
+static void post_sb_notification(struct super_block *s, struct superblock_notification *n)
+{
+ post_watch_notification(s->s_watchers, &n->watch, current_cred(),
+ s->s_unique_id);
+}
+
+/*
+ * Post simple superblock notification.
+ */
+void __notify_sb(struct super_block *s,
+ enum superblock_notification_type subtype,
+ u32 info)
+{
+ struct superblock_notification n = {
+ .watch.type = WATCH_TYPE_SB_NOTIFY,
+ .watch.subtype = subtype,
+ .watch.info = watch_sizeof(n) | info,
+ .sb_id = s->s_unique_id,
+ };
+
+ post_sb_notification(s, &n);
+}
+
+/*
+ * Post superblock error notification.
+ */
+void __notify_sb_error(struct super_block *s, int error)
+{
+ struct superblock_error_notification n = {
+ .s.watch.type = WATCH_TYPE_SB_NOTIFY,
+ .s.watch.subtype = NOTIFY_SUPERBLOCK_ERROR,
+ .s.watch.info = watch_sizeof(n),
+ .s.sb_id = s->s_unique_id,
+ .error_number = error,
+ .error_cookie = 0,
+ };
+
+ post_sb_notification(s, &n.s);
+}
+
+/*
+ * Post superblock quota overrun notification.
+ */
+void __notify_sb_EQDUOT(struct super_block *s)
+{
+ struct superblock_notification n = {
+ .watch.type = WATCH_TYPE_SB_NOTIFY,
+ .watch.subtype = NOTIFY_SUPERBLOCK_EDQUOT,
+ .watch.info = watch_sizeof(n),
+ .sb_id = s->s_unique_id,
+ };
+
+ post_sb_notification(s, &n);
+}
+
+static void sb_release_watch(struct watch *watch)
+{
+ put_super(watch->private);
+}
+
+/**
+ * sys_watch_sb - Watch for superblock events.
+ * @dfd: Base directory to pathwalk from or fd referring to superblock.
+ * @filename: Path to superblock to place the watch upon
+ * @at_flags: Pathwalk control flags
+ * @watch_fd: The watch queue to send notifications to.
+ * @watch_id: The watch ID to be placed in the notification (-1 to remove watch)
+ */
+SYSCALL_DEFINE5(watch_sb,
+ int, dfd,
+ const char __user *, filename,
+ unsigned int, at_flags,
+ int, watch_fd,
+ int, watch_id)
+{
+ struct watch_queue *wqueue;
+ struct super_block *s;
+ struct watch_list *wlist = NULL;
+ struct watch *watch = NULL;
+ struct path path;
+ unsigned int lookup_flags =
+ LOOKUP_DIRECTORY | LOOKUP_FOLLOW | LOOKUP_AUTOMOUNT;
+ bool drop_s_count = false;
+ int ret;
+
+ if (watch_id < -1 || watch_id > 0xff)
+ return -EINVAL;
+ if ((at_flags & ~(AT_NO_AUTOMOUNT | AT_EMPTY_PATH)) != 0)
+ return -EINVAL;
+ if (at_flags & AT_NO_AUTOMOUNT)
+ lookup_flags &= ~LOOKUP_AUTOMOUNT;
+ if (at_flags & AT_EMPTY_PATH)
+ lookup_flags |= LOOKUP_EMPTY;
+
+ ret = user_path_at(dfd, filename, at_flags, &path);
+ if (ret)
+ return ret;
+
+ ret = inode_permission(path.dentry->d_inode, MAY_EXEC);
+ if (ret)
+ goto err_path;
+
+ wqueue = get_watch_queue(watch_fd);
+ if (IS_ERR(wqueue))
+ goto err_path;
+
+ s = path.dentry->d_sb;
+ if (watch_id >= 0) {
+ ret = -ENOMEM;
+ if (!READ_ONCE(s->s_watchers)) {
+ wlist = kzalloc(sizeof(*wlist), GFP_KERNEL);
+ if (!wlist)
+ goto err_wqueue;
+ init_watch_list(wlist, sb_release_watch);
+ }
+
+ watch = kzalloc(sizeof(*watch), GFP_KERNEL);
+ if (!watch)
+ goto err_wlist;
+
+ init_watch(watch, wqueue);
+ watch->id = s->s_unique_id;
+ watch->private = s;
+ watch->info_id = (u32)watch_id << 24;
+
+ ret = security_watch_sb(watch, s);
+ if (ret < 0)
+ goto err_watch;
+
+ down_write(&s->s_umount);
+ ret = -EIO;
+ if (atomic_read(&s->s_active)) {
+ if (!s->s_watchers) {
+ s->s_watchers = wlist;
+ wlist = NULL;
+ }
+
+ spin_lock(&sb_lock);
+ s->s_count++;
+ spin_unlock(&sb_lock);
+ ret = add_watch_to_object(watch, s->s_watchers);
+ if (ret == 0)
+ watch = NULL; /* It worked */
+ else
+ drop_s_count = true;
+ }
+ up_write(&s->s_umount);
+ if (drop_s_count)
+ put_super(s);
+ } else {
+ ret = -EBADSLT;
+ down_write(&s->s_umount);
+ ret = remove_watch_from_object(s->s_watchers, wqueue,
+ s->s_unique_id, false);
+ up_write(&s->s_umount);
+ }
+
+err_watch:
+ kfree(watch);
+err_wlist:
+ kfree(wlist);
+err_wqueue:
+ put_watch_queue(wqueue);
+err_path:
+ path_put(&path);
+ return ret;
+}
+#endif
@@ -40,6 +40,7 @@
#include <linux/fs_types.h>
#include <linux/build_bug.h>
#include <linux/stddef.h>
+#include <linux/watch_queue.h>
#include <asm/byteorder.h>
#include <uapi/linux/fs.h>
@@ -1551,6 +1552,12 @@ struct super_block {
/* Superblock event notifications */
u64 s_unique_id;
+
+#ifdef CONFIG_SB_NOTIFICATIONS
+ struct watch_list *s_watchers;
+#endif
+ atomic_t s_change_counter; /* Count of config change notifications */
+ atomic_t s_notify_counter; /* Count of other notifications */
} __randomize_layout;
/* Helper functions so that in most cases filesystems will
@@ -3654,4 +3661,56 @@ static inline int inode_drain_writes(struct inode *inode)
return filemap_write_and_wait(inode->i_mapping);
}
+extern void __notify_sb(struct super_block *s,
+ enum superblock_notification_type subtype,
+ u32 info);
+extern void __notify_sb_error(struct super_block *s, int error);
+extern void __notify_sb_EQDUOT(struct super_block *s);
+
+/**
+ * notify_sb: Post simple superblock notification.
+ * @s: The superblock the notification is about.
+ * @subtype: The type of notification.
+ * @info: WATCH_INFO_FLAG_* flags to be set in the record.
+ */
+static inline void notify_sb(struct super_block *s,
+ enum superblock_notification_type subtype,
+ u32 info)
+{
+#ifdef CONFIG_SB_NOTIFICATIONS
+ atomic_inc(&s->s_change_counter);
+ if (unlikely(READ_ONCE(s->s_watchers)))
+ __notify_sb(s, subtype, info);
+#endif
+}
+
+/**
+ * notify_sb_error: Post superblock error notification.
+ * @s: The superblock the notification is about.
+ * @error: The error number to be recorded.
+ */
+static inline int notify_sb_error(struct super_block *s, int error)
+{
+#ifdef CONFIG_SB_NOTIFICATIONS
+ atomic_inc(&s->s_notify_counter);
+ if (unlikely(READ_ONCE(s->s_watchers)))
+ __notify_sb_error(s, error);
+#endif
+ return error;
+}
+
+/**
+ * notify_sb_EDQUOT: Post superblock quota overrun notification.
+ * @s: The superblock the notification is about.
+ */
+static inline int notify_sb_EQDUOT(struct super_block *s)
+{
+#ifdef CONFIG_SB_NOTIFICATIONS
+ atomic_inc(&s->s_notify_counter);
+ if (unlikely(READ_ONCE(s->s_watchers)))
+ __notify_sb_EQDUOT(s);
+#endif
+ return -EDQUOT;
+}
+
#endif /* _LINUX_FS_H */
@@ -1005,6 +1005,8 @@ asmlinkage long sys_pidfd_send_signal(int pidfd, int sig,
asmlinkage long sys_pidfd_getfd(int pidfd, int fd, unsigned int flags);
asmlinkage long sys_watch_mount(int dfd, const char __user *path,
unsigned int at_flags, int watch_fd, int watch_id);
+asmlinkage long sys_watch_sb(int dfd, const char __user *path,
+ unsigned int at_flags, int watch_fd, int watch_id);
/*
* Architecture-specific system calls
@@ -857,9 +857,11 @@ __SYSCALL(__NR_openat2, sys_openat2)
__SYSCALL(__NR_pidfd_getfd, sys_pidfd_getfd)
#define __NR_watch_mount 439
__SYSCALL(__NR_watch_mount, sys_watch_mount)
+#define __NR_watch_sb 440
+__SYSCALL(__NR_watch_sb, sys_watch_sb)
#undef __NR_syscalls
-#define __NR_syscalls 440
+#define __NR_syscalls 441
/*
* 32 bit systems traditionally used different
@@ -15,7 +15,8 @@ enum watch_notification_type {
WATCH_TYPE_META = 0, /* Special record */
WATCH_TYPE_KEY_NOTIFY = 1, /* Key change event notification */
WATCH_TYPE_MOUNT_NOTIFY = 2, /* Mount topology change notification */
- WATCH_TYPE___NR = 3
+ WATCH_TYPE_SB_NOTIFY = 3, /* Superblock event notification */
+ WATCH_TYPE___NR = 4
};
enum watch_meta_notification_subtype {
@@ -135,4 +136,32 @@ struct mount_notification {
__u32 __padding;
};
+/*
+ * Type of superblock notification.
+ */
+enum superblock_notification_type {
+ NOTIFY_SUPERBLOCK_READONLY = 0, /* Filesystem toggled between R/O and R/W */
+ NOTIFY_SUPERBLOCK_ERROR = 1, /* Error in filesystem or blockdev */
+ NOTIFY_SUPERBLOCK_EDQUOT = 2, /* EDQUOT notification */
+ NOTIFY_SUPERBLOCK_NETWORK = 3, /* Network status change */
+};
+
+#define NOTIFY_SUPERBLOCK_IS_NOW_RO WATCH_INFO_FLAG_0 /* Superblock changed to R/O */
+
+/*
+ * Superblock notification record.
+ * - watch.type = WATCH_TYPE_MOUNT_NOTIFY
+ * - watch.subtype = enum superblock_notification_subtype
+ */
+struct superblock_notification {
+ struct watch_notification watch; /* WATCH_TYPE_SB_NOTIFY */
+ __u64 sb_id; /* 64-bit superblock ID */
+};
+
+struct superblock_error_notification {
+ struct superblock_notification s; /* subtype = notify_superblock_error */
+ __u32 error_number;
+ __u32 error_cookie;
+};
+
#endif /* _UAPI_LINUX_WATCH_QUEUE_H */
@@ -119,6 +119,9 @@ COND_SYSCALL_COMPAT(signalfd4);
/* fs/sync.c */
+/* fs/super.c */
+COND_SYSCALL(watch_sb);
+
/* fs/timerfd.c */
COND_SYSCALL(timerfd_create);
COND_SYSCALL(timerfd_settime);
Add a superblock event notification facility whereby notifications about superblock events, such as I/O errors (EIO), quota limits being hit (EDQUOT) and running out of space (ENOSPC) can be reported to a monitoring process asynchronously. Note that this does not cover vfsmount topology changes. watch_mount() is used for that. Firstly, a watch queue needs to be created: pipe2(fds, O_NOTIFICATION_PIPE); ioctl(fds[1], IOC_WATCH_QUEUE_SET_SIZE, 256); then a notification can be set up to report notifications via that queue: struct watch_notification_filter filter = { .nr_filters = 1, .filters = { [0] = { .type = WATCH_TYPE_SB_NOTIFY, .subtype_filter[0] = UINT_MAX, }, }, }; ioctl(fds[1], IOC_WATCH_QUEUE_SET_FILTER, &filter); watch_sb(AT_FDCWD, "/home/dhowells", 0, fds[1], 0x03); In this case, it would let me monitor my own homedir for events. After setting the watch, records will be placed into the queue when, for example, as superblock switches between read-write and read-only. Records are of the following format: struct superblock_notification { struct watch_notification watch; __u64 sb_id; } *n; Where: n->watch.type will be WATCH_TYPE_SB_NOTIFY. n->watch.subtype will indicate the type of event, such as NOTIFY_SUPERBLOCK_READONLY. n->watch.info & WATCH_INFO_LENGTH will indicate the length of the record. n->watch.info & WATCH_INFO_ID will be the fifth argument to watch_sb(), shifted. n->watch.info & NOTIFY_SUPERBLOCK_IS_NOW_RO will be used for NOTIFY_SUPERBLOCK_READONLY, being set if the superblock becomes R/O, and being cleared otherwise. n->sb_id will be the ID of the superblock, as can be retrieved with the fsinfo() syscall, as part of the fsinfo_sb_notifications attribute in the the watch_id field. Note that it is permissible for event records to be of variable length - or, at least, the length may be dependent on the subtype. Note also that the queue can be shared between multiple notifications of various types. Signed-off-by: David Howells <dhowells@redhat.com> --- Documentation/watch_queue.rst | 12 ++ arch/alpha/kernel/syscalls/syscall.tbl | 1 arch/arm/tools/syscall.tbl | 1 arch/arm64/include/asm/unistd.h | 2 arch/arm64/include/asm/unistd32.h | 2 arch/ia64/kernel/syscalls/syscall.tbl | 1 arch/m68k/kernel/syscalls/syscall.tbl | 1 arch/microblaze/kernel/syscalls/syscall.tbl | 1 arch/mips/kernel/syscalls/syscall_n32.tbl | 1 arch/mips/kernel/syscalls/syscall_n64.tbl | 1 arch/mips/kernel/syscalls/syscall_o32.tbl | 1 arch/parisc/kernel/syscalls/syscall.tbl | 1 arch/powerpc/kernel/syscalls/syscall.tbl | 1 arch/s390/kernel/syscalls/syscall.tbl | 1 arch/sh/kernel/syscalls/syscall.tbl | 1 arch/sparc/kernel/syscalls/syscall.tbl | 1 arch/x86/entry/syscalls/syscall_32.tbl | 1 arch/x86/entry/syscalls/syscall_64.tbl | 1 arch/xtensa/kernel/syscalls/syscall.tbl | 1 fs/Kconfig | 12 ++ fs/super.c | 181 +++++++++++++++++++++++++++ include/linux/fs.h | 59 +++++++++ include/linux/syscalls.h | 2 include/uapi/asm-generic/unistd.h | 4 - include/uapi/linux/watch_queue.h | 31 ++++- kernel/sys_ni.c | 3 26 files changed, 321 insertions(+), 3 deletions(-)