[PATCH] um: ubd: Add REQ_FLUSH suppport

Richard Weinberger
2013-08-17T22:09:53Z

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.

Cc: rjones@redhat.com
Signed-off-by: Richard Weinberger <richard@nod.at>
---
arch/um/drivers/ubd_kern.c | 41 ++++++++++++++++++++++++++++++++++++++++-
arch/um/include/shared/os.h | 1 +
arch/um/os-Linux/file.c | 9 +++++++++
3 files changed, 50 insertions(+), 1 deletion(-)

diff --git a/arch/um/drivers/ubd_kern.c b/arch/um/drivers/ubd_kern.c
index 879990c..d27c703 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 95feaa4..04859b7 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 c17bd6f..07a7501 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;
--
1.8.3.1