CIFS: Add support for direct I/O write

With direct I/O write, user supplied buffers are pinned to the memory and data
are transferred directly from user buffers to the transport layer.

Change in v3: add support for kernel AIO

Change in v4:
Refactor common write code to __cifs_writev for direct and non-direct I/O.
Retry on direct I/O failure.

Signed-off-by: Long Li <longli@microsoft.com>
Signed-off-by: Steve French <stfrench@microsoft.com>

2 files changed, 164 insertions, 41 deletions

diff --git a/fs/cifs/cifsfs.h b/fs/cifs/cifsfs.h
index 3abea1a3f20c..4c3b5cfccc49 100644
--- a/fs/cifs/cifsfs.h
+++ b/fs/cifs/cifsfs.h
@@ -104,6 +104,7 @@ extern ssize_t cifs_user_readv(struct kiocb *iocb, struct iov_iter *to);
 extern ssize_t cifs_direct_readv(struct kiocb *iocb, struct iov_iter *to);
 extern ssize_t cifs_strict_readv(struct kiocb *iocb, struct iov_iter *to);
 extern ssize_t cifs_user_writev(struct kiocb *iocb, struct iov_iter *from);
+extern ssize_t cifs_direct_writev(struct kiocb *iocb, struct iov_iter *from);
 extern ssize_t cifs_strict_writev(struct kiocb *iocb, struct iov_iter *from);
 extern int cifs_lock(struct file *, int, struct file_lock *);
 extern int cifs_fsync(struct file *, loff_t, loff_t, int);
diff --git a/fs/cifs/file.c b/fs/cifs/file.c
index 1be36076e960..937ffa79066b 100644
--- a/fs/cifs/file.c
+++ b/fs/cifs/file.c
@@ -2538,6 +2538,61 @@ wdata_fill_from_iovec(struct cifs_writedata *wdata, struct iov_iter *from,
 }
 
 static int
+cifs_resend_wdata(struct cifs_writedata *wdata, struct list_head *wdata_list,
+        struct cifs_aio_ctx *ctx)
+{
+        int wait_retry = 0;
+        unsigned int wsize, credits;
+        int rc;
+        struct TCP_Server_Info *server =
+                tlink_tcon(wdata->cfile->tlink)->ses->server;
+
+        /*
+         * Try to resend this wdata, waiting for credits up to 3 seconds.
+         * Note: we are attempting to resend the whole wdata not in segments
+         */
+        do {
+                rc = server->ops->wait_mtu_credits(
+                        server, wdata->bytes, &wsize, &credits);
+
+                if (rc)
+                        break;
+
+                if (wsize < wdata->bytes) {
+                        add_credits_and_wake_if(server, credits, 0);
+                        msleep(1000);
+                        wait_retry++;
+                }
+        } while (wsize < wdata->bytes && wait_retry < 3);
+
+        if (wsize < wdata->bytes) {
+                rc = -EBUSY;
+                goto out;
+        }
+
+        rc = -EAGAIN;
+        while (rc == -EAGAIN) {
+                rc = 0;
+                if (wdata->cfile->invalidHandle)
+                        rc = cifs_reopen_file(wdata->cfile, false);
+                if (!rc)
+                        rc = server->ops->async_writev(wdata,
+                                        cifs_uncached_writedata_release);
+        }
+
+        if (!rc) {
+                list_add_tail(&wdata->list, wdata_list);
+                return 0;
+        }
+
+        add_credits_and_wake_if(server, wdata->credits, 0);
+out:
+        kref_put(&wdata->refcount, cifs_uncached_writedata_release);
+
+        return rc;
+}
+
+static int
 cifs_write_from_iter(loff_t offset, size_t len, struct iov_iter *from,
                      struct cifsFileInfo *open_file,
                      struct cifs_sb_info *cifs_sb, struct list_head *wdata_list,
@@ -2551,6 +2606,8 @@ cifs_write_from_iter(loff_t offset, size_t len, struct iov_iter *from,
         loff_t saved_offset = offset;
         pid_t pid;
         struct TCP_Server_Info *server;
+        struct page **pagevec;
+        size_t start;
 
         if (cifs_sb->mnt_cifs_flags & CIFS_MOUNT_RWPIDFORWARD)
                 pid = open_file->pid;
@@ -2567,38 +2624,76 @@ cifs_write_from_iter(loff_t offset, size_t len, struct iov_iter *from,
                 if (rc)
                         break;
 
-                nr_pages = get_numpages(wsize, len, &cur_len);
-                wdata = cifs_writedata_alloc(nr_pages,
+                if (ctx->direct_io) {
+                        cur_len = iov_iter_get_pages_alloc(
+                                from, &pagevec, wsize, &start);
+                        if (cur_len < 0) {
+                                cifs_dbg(VFS,
+                                        "direct_writev couldn't get user pages "
+                                        "(rc=%zd) iter type %d iov_offset %zd "
+                                        "count %zd\n",
+                                        cur_len, from->type,
+                                        from->iov_offset, from->count);
+                                dump_stack();
+                                break;
+                        }
+                        iov_iter_advance(from, cur_len);
+
+                        nr_pages =
+                                (cur_len + start + PAGE_SIZE - 1) / PAGE_SIZE;
+
+                        wdata = cifs_writedata_direct_alloc(pagevec,
                                              cifs_uncached_writev_complete);
-                if (!wdata) {
-                        rc = -ENOMEM;
-                        add_credits_and_wake_if(server, credits, 0);
-                        break;
-                }
+                        if (!wdata) {
+                                rc = -ENOMEM;
+                                add_credits_and_wake_if(server, credits, 0);
+                                break;
+                        }
 
-                rc = cifs_write_allocate_pages(wdata->pages, nr_pages);
-                if (rc) {
-                        kfree(wdata);
-                        add_credits_and_wake_if(server, credits, 0);
-                        break;
-                }
 
-                num_pages = nr_pages;
-                rc = wdata_fill_from_iovec(wdata, from, &cur_len, &num_pages);
-                if (rc) {
-                        for (i = 0; i < nr_pages; i++)
-                                put_page(wdata->pages[i]);
-                        kfree(wdata);
-                        add_credits_and_wake_if(server, credits, 0);
-                        break;
-                }
+                        wdata->page_offset = start;
+                        wdata->tailsz =
+                                nr_pages > 1 ?
+                                        cur_len - (PAGE_SIZE - start) -
+                                        (nr_pages - 2) * PAGE_SIZE :
+                                        cur_len;
+                } else {
+                        nr_pages = get_numpages(wsize, len, &cur_len);
+                        wdata = cifs_writedata_alloc(nr_pages,
+                                             cifs_uncached_writev_complete);
+                        if (!wdata) {
+                                rc = -ENOMEM;
+                                add_credits_and_wake_if(server, credits, 0);
+                                break;
+                        }
 
-                /*
-                 * Bring nr_pages down to the number of pages we actually used,
-                 * and free any pages that we didn't use.
-                 */
-                for ( ; nr_pages > num_pages; nr_pages--)
-                        put_page(wdata->pages[nr_pages - 1]);
+                        rc = cifs_write_allocate_pages(wdata->pages, nr_pages);
+                        if (rc) {
+                                kfree(wdata);
+                                add_credits_and_wake_if(server, credits, 0);
+                                break;
+                        }
+
+                        num_pages = nr_pages;
+                        rc = wdata_fill_from_iovec(
+                                wdata, from, &cur_len, &num_pages);
+                        if (rc) {
+                                for (i = 0; i < nr_pages; i++)
+                                        put_page(wdata->pages[i]);
+                                kfree(wdata);
+                                add_credits_and_wake_if(server, credits, 0);
+                                break;
+                        }
+
+                        /*
+                         * Bring nr_pages down to the number of pages we
+                         * actually used, and free any pages that we didn't use.
+                         */
+                        for ( ; nr_pages > num_pages; nr_pages--)
+                                put_page(wdata->pages[nr_pages - 1]);
+
+                        wdata->tailsz = cur_len - ((nr_pages - 1) * PAGE_SIZE);
+                }
 
                 wdata->sync_mode = WB_SYNC_ALL;
                 wdata->nr_pages = nr_pages;
@@ -2607,7 +2702,6 @@ cifs_write_from_iter(loff_t offset, size_t len, struct iov_iter *from,
                 wdata->pid = pid;
                 wdata->bytes = cur_len;
                 wdata->pagesz = PAGE_SIZE;
-                wdata->tailsz = cur_len - ((nr_pages - 1) * PAGE_SIZE);
                 wdata->credits = credits;
                 wdata->ctx = ctx;
                 kref_get(&ctx->refcount);
@@ -2682,13 +2776,18 @@ restart_loop:
                                 INIT_LIST_HEAD(&tmp_list);
                                 list_del_init(&wdata->list);
 
-                                iov_iter_advance(&tmp_from,
+                                if (ctx->direct_io)
+                                        rc = cifs_resend_wdata(
+                                                wdata, &tmp_list, ctx);
+                                else {
+                                        iov_iter_advance(&tmp_from,
                                                  wdata->offset - ctx->pos);
 
-                                rc = cifs_write_from_iter(wdata->offset,
+                                        rc = cifs_write_from_iter(wdata->offset,
                                                 wdata->bytes, &tmp_from,
                                                 ctx->cfile, cifs_sb, &tmp_list,
                                                 ctx);
+                                }
 
                                 list_splice(&tmp_list, &ctx->list);
 
@@ -2701,8 +2800,9 @@ restart_loop:
                 kref_put(&wdata->refcount, cifs_uncached_writedata_release);
         }
 
-        for (i = 0; i < ctx->npages; i++)
-                put_page(ctx->bv[i].bv_page);
+        if (!ctx->direct_io)
+                for (i = 0; i < ctx->npages; i++)
+                        put_page(ctx->bv[i].bv_page);
 
         cifs_stats_bytes_written(tcon, ctx->total_len);
         set_bit(CIFS_INO_INVALID_MAPPING, &CIFS_I(dentry->d_inode)->flags);
@@ -2717,7 +2817,8 @@ restart_loop:
                 complete(&ctx->done);
 }
 
-ssize_t cifs_user_writev(struct kiocb *iocb, struct iov_iter *from)
+static ssize_t __cifs_writev(
+        struct kiocb *iocb, struct iov_iter *from, bool direct)
 {
         struct file *file = iocb->ki_filp;
         ssize_t total_written = 0;
@@ -2726,13 +2827,18 @@ ssize_t cifs_user_writev(struct kiocb *iocb, struct iov_iter *from)
         struct cifs_sb_info *cifs_sb;
         struct cifs_aio_ctx *ctx;
         struct iov_iter saved_from = *from;
+        size_t len = iov_iter_count(from);
         int rc;
 
         /*
-         * BB - optimize the way when signing is disabled. We can drop this
-         * extra memory-to-memory copying and use iovec buffers for constructing
-         * write request.
+         * iov_iter_get_pages_alloc doesn't work with ITER_KVEC.
+         * In this case, fall back to non-direct write function.
+         * this could be improved by getting pages directly in ITER_KVEC
          */
+        if (direct && from->type & ITER_KVEC) {
+                cifs_dbg(FYI, "use non-direct cifs_writev for kvec I/O\n");
+                direct = false;
+        }
 
         rc = generic_write_checks(iocb, from);
         if (rc <= 0)
@@ -2756,10 +2862,16 @@ ssize_t cifs_user_writev(struct kiocb *iocb, struct iov_iter *from)
 
         ctx->pos = iocb->ki_pos;
 
-        rc = setup_aio_ctx_iter(ctx, from, WRITE);
-        if (rc) {
-                kref_put(&ctx->refcount, cifs_aio_ctx_release);
-                return rc;
+        if (direct) {
+                ctx->direct_io = true;
+                ctx->iter = *from;
+                ctx->len = len;
+        } else {
+                rc = setup_aio_ctx_iter(ctx, from, WRITE);
+                if (rc) {
+                        kref_put(&ctx->refcount, cifs_aio_ctx_release);
+                        return rc;
+                }
         }
 
         /* grab a lock here due to read response handlers can access ctx */
@@ -2809,6 +2921,16 @@ ssize_t cifs_user_writev(struct kiocb *iocb, struct iov_iter *from)
         return total_written;
 }
 
+ssize_t cifs_direct_writev(struct kiocb *iocb, struct iov_iter *from)
+{
+        return __cifs_writev(iocb, from, true);
+}
+
+ssize_t cifs_user_writev(struct kiocb *iocb, struct iov_iter *from)
+{
+        return __cifs_writev(iocb, from, false);
+}
+
 static ssize_t
 cifs_writev(struct kiocb *iocb, struct iov_iter *from)
 {