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Registered in England and Wales under Company Registration No. 3798903 Subject: [PATCH 03/17] watch_queue: sample: Display mount tree change notifications [ver #17] From: David Howells To: viro@zeniv.linux.org.uk Cc: dhowells@redhat.com, raven@themaw.net, mszeredi@redhat.com, christian@brauner.io, jannh@google.com, darrick.wong@oracle.com, linux-api@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org Date: Fri, 21 Feb 2020 18:02:10 +0000 Message-ID: <158230813054.2185128.14599796644062916018.stgit@warthog.procyon.org.uk> In-Reply-To: <158230810644.2185128.16726948836367716086.stgit@warthog.procyon.org.uk> References: <158230810644.2185128.16726948836367716086.stgit@warthog.procyon.org.uk> User-Agent: StGit/0.21 MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit X-Scanned-By: MIMEDefang 2.79 on 10.5.11.15 Sender: linux-fsdevel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org This is run like: ./watch_test and watches "/" for changes to the mount topology and the attributes of individual mount objects. # mount -t tmpfs none /mnt # mount -o remount,ro /mnt # mount -o remount,rw /mnt producing: # ./watch_test read() = 16 NOTIFY[000]: ty=000002 sy=00 i=02000010 MOUNT 00000060 change=0[new_mount] aux=416 read() = 16 NOTIFY[000]: ty=000002 sy=04 i=02010010 MOUNT 000001a0 change=4[setattr] aux=0 read() = 16 NOTIFY[000]: ty=000002 sy=04 i=02010010 MOUNT 000001a0 change=4[setattr] aux=0 Signed-off-by: David Howells --- samples/watch_queue/watch_test.c | 39 +++++++++++++++++++++++++++++++++++++- 1 file changed, 38 insertions(+), 1 deletion(-) diff --git a/samples/watch_queue/watch_test.c b/samples/watch_queue/watch_test.c index 0eaff5dc04c3..49d185150506 100644 --- a/samples/watch_queue/watch_test.c +++ b/samples/watch_queue/watch_test.c @@ -26,6 +26,9 @@ #ifndef __NR_watch_devices #define __NR_watch_devices -1 #endif +#ifndef __NR_watch_mount +#define __NR_watch_mount -1 +#endif #define BUF_SIZE 256 @@ -58,6 +61,27 @@ static void saw_key_change(struct watch_notification *n, size_t len) k->key_id, n->subtype, key_subtypes[n->subtype], k->aux); } +static const char *mount_subtypes[256] = { + [NOTIFY_MOUNT_NEW_MOUNT] = "new_mount", + [NOTIFY_MOUNT_UNMOUNT] = "unmount", + [NOTIFY_MOUNT_EXPIRY] = "expiry", + [NOTIFY_MOUNT_READONLY] = "readonly", + [NOTIFY_MOUNT_SETATTR] = "setattr", + [NOTIFY_MOUNT_MOVE_FROM] = "move_from", + [NOTIFY_MOUNT_MOVE_TO] = "move_to", +}; + +static void saw_mount_change(struct watch_notification *n, size_t len) +{ + struct mount_notification *m = (struct mount_notification *)n; + + if (len != sizeof(struct mount_notification)) + return; + + printf("MOUNT %08x change=%u[%s] aux=%u\n", + m->triggered_on, n->subtype, mount_subtypes[n->subtype], m->changed_mount); +} + /* * Consume and display events. */ @@ -134,6 +158,9 @@ static void consumer(int fd) default: printf("other type\n"); break; + case WATCH_TYPE_MOUNT_NOTIFY: + saw_mount_change(&n.n, len); + break; } p += len; @@ -142,12 +169,17 @@ static void consumer(int fd) } static struct watch_notification_filter filter = { - .nr_filters = 1, + .nr_filters = 2, .filters = { [0] = { .type = WATCH_TYPE_KEY_NOTIFY, .subtype_filter[0] = UINT_MAX, }, + [1] = { + .type = WATCH_TYPE_MOUNT_NOTIFY, + // Reject move-from notifications + .subtype_filter[0] = UINT_MAX & ~(1 << NOTIFY_MOUNT_MOVE_FROM), + }, }, }; @@ -181,6 +213,11 @@ int main(int argc, char **argv) exit(1); } + if (syscall(__NR_watch_mount, AT_FDCWD, "/", 0, fd, 0x02) == -1) { + perror("watch_mount"); + exit(1); + } + consumer(fd); exit(0); }