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>

diff --git a/arch/um/drivers/ubd_kern.c b/arch/um/drivers/ubd_kern.c
index 879990cb66c6264e4db70e4ed812a1710ea6b1df..d27c703be1a13eba5f0ca91a5561e24fbd26b494 100644 (file)
--- 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]);
@@ -1238,6 +1239,19 @@ 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)
 {
@@ -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 c70a234a3f8c7d4a31938963ef01ba167526d78d..e98303925cc5dee7da40e7f508ec78c480779fcc 100644 (file)
--- 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 c17bd6f7d674d98ad745ffb21c0ccab11fd515b9..07a750197bb09d3b5ce59b631aed874d58603386 100644 (file)
--- 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;