um: ubd: Add REQ_FLUSH suppport

UML's block device driver does not support write barriers,
to support this this patch adds REQ_FLUSH suppport.
Every time the block layer sends a REQ_FLUSH we fsync() now
our backing file to guarantee data consistency.

Reported-and-tested-by: Richard W.M. Jones <rjones@redhat.com>
Signed-off-by: Richard Weinberger <richard@nod.at>

3 files changed, 50 insertions, 1 deletions

diff --git a/arch/um/drivers/ubd_kern.c b/arch/um/drivers/ubd_kern.c
index 879990cb66c6..d27c703be1a1 100644
--- a/arch/um/drivers/ubd_kern.c
+++ b/arch/um/drivers/ubd_kern.c
@@ -41,7 +41,7 @@
 #include <os.h>
 #include "cow.h"
 
-enum ubd_req { UBD_READ, UBD_WRITE };
+enum ubd_req { UBD_READ, UBD_WRITE, UBD_FLUSH };
 
 struct io_thread_req {
         struct request *req;
@@ -866,6 +866,7 @@ static int ubd_add(int n, char **error_out)
                 goto out;
         }
         ubd_dev->queue->queuedata = ubd_dev;
+        blk_queue_flush(ubd_dev->queue, REQ_FLUSH);
 
         blk_queue_max_segments(ubd_dev->queue, MAX_SG);
         err = ubd_disk_register(UBD_MAJOR, ubd_dev->size, n, &ubd_gendisk[n]);
@@ -1239,6 +1240,19 @@ static void prepare_request(struct request *req, struct io_thread_req *io_req,
 }
 
 /* Called with dev->lock held */
+static void prepare_flush_request(struct request *req,
+                                  struct io_thread_req *io_req)
+{
+        struct gendisk *disk = req->rq_disk;
+        struct ubd *ubd_dev = disk->private_data;
+
+        io_req->req = req;
+        io_req->fds[0] = (ubd_dev->cow.file != NULL) ? ubd_dev->cow.fd :
+                ubd_dev->fd;
+        io_req->op = UBD_FLUSH;
+}
+
+/* Called with dev->lock held */
 static void do_ubd_request(struct request_queue *q)
 {
         struct io_thread_req *io_req;
@@ -1259,6 +1273,20 @@ static void do_ubd_request(struct request_queue *q)
                 }
 
                 req = dev->request;
+
+                if (req->cmd_flags & REQ_FLUSH) {
+                        io_req = kmalloc(sizeof(struct io_thread_req),
+                                         GFP_ATOMIC);
+                        if (io_req == NULL) {
+                                if (list_empty(&dev->restart))
+                                        list_add(&dev->restart, &restart);
+                                return;
+                        }
+                        prepare_flush_request(req, io_req);
+                        os_write_file(thread_fd, &io_req,
+                                          sizeof(struct io_thread_req *));
+                }
+
                 while(dev->start_sg < dev->end_sg){
                         struct scatterlist *sg = &dev->sg[dev->start_sg];
 
@@ -1367,6 +1395,17 @@ static void do_io(struct io_thread_req *req)
         int err;
         __u64 off;
 
+        if (req->op == UBD_FLUSH) {
+                /* fds[0] is always either the rw image or our cow file */
+                n = os_sync_file(req->fds[0]);
+                if (n != 0) {
+                        printk("do_io - sync failed err = %d "
+                               "fd = %d\n", -n, req->fds[0]);
+                        req->error = 1;
+                }
+                return;
+        }
+
         nsectors = req->length / req->sectorsize;
         start = 0;
         do {
diff --git a/arch/um/include/shared/os.h b/arch/um/include/shared/os.h
index c70a234a3f8c..e98303925cc5 100644
--- a/arch/um/include/shared/os.h
+++ b/arch/um/include/shared/os.h
@@ -141,6 +141,7 @@ extern int os_seek_file(int fd, unsigned long long offset);
 extern int os_open_file(const char *file, struct openflags flags, int mode);
 extern int os_read_file(int fd, void *buf, int len);
 extern int os_write_file(int fd, const void *buf, int count);
+extern int os_sync_file(int fd);
 extern int os_file_size(const char *file, unsigned long long *size_out);
 extern int os_file_modtime(const char *file, unsigned long *modtime);
 extern int os_pipe(int *fd, int stream, int close_on_exec);
diff --git a/arch/um/os-Linux/file.c b/arch/um/os-Linux/file.c
index c17bd6f7d674..07a750197bb0 100644
--- a/arch/um/os-Linux/file.c
+++ b/arch/um/os-Linux/file.c
@@ -266,6 +266,15 @@ int os_write_file(int fd, const void *buf, int len)
         return n;
 }
 
+int os_sync_file(int fd)
+{
+        int n = fsync(fd);
+
+        if (n < 0)
+                return -errno;
+        return n;
+}
+
 int os_file_size(const char *file, unsigned long long *size_out)
 {
         struct uml_stat buf;