fuse: implement perform_write

Introduce fuse_perform_write.  With fusexmp (a passthrough filesystem), large
(1MB) writes into a backing tmpfs filesystem are sped up by almost 4 times
(256MB/s vs 71MB/s).

[mszeredi@suse.cz]:

 - split into smaller functions
 - testing
 - duplicate generic_file_aio_write(), so that there's no need to add a
   new ->perform_write() a_op.  Comment from hch.

Signed-off-by: Nick Piggin <npiggin@suse.de>
Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>
Cc: Christoph Hellwig <hch@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 193 insertions, 1 deletions

diff --git a/fs/fuse/file.c b/fs/fuse/file.c
index f0f0f278b4ea..c5b5982bf386 100644
--- a/fs/fuse/file.c
+++ b/fs/fuse/file.c
@@ -677,6 +677,198 @@ static int fuse_write_end(struct file *file, struct address_space *mapping,
         return res;
 }
 
+static size_t fuse_send_write_pages(struct fuse_req *req, struct file *file,
+                                    struct inode *inode, loff_t pos,
+                                    size_t count)
+{
+        size_t res;
+        unsigned offset;
+        unsigned i;
+
+        for (i = 0; i < req->num_pages; i++)
+                fuse_wait_on_page_writeback(inode, req->pages[i]->index);
+
+        res = fuse_send_write(req, file, inode, pos, count, NULL);
+
+        offset = req->page_offset;
+        count = res;
+        for (i = 0; i < req->num_pages; i++) {
+                struct page *page = req->pages[i];
+
+                if (!req->out.h.error && !offset && count >= PAGE_CACHE_SIZE)
+                        SetPageUptodate(page);
+
+                if (count > PAGE_CACHE_SIZE - offset)
+                        count -= PAGE_CACHE_SIZE - offset;
+                else
+                        count = 0;
+                offset = 0;
+
+                unlock_page(page);
+                page_cache_release(page);
+        }
+
+        return res;
+}
+
+static ssize_t fuse_fill_write_pages(struct fuse_req *req,
+                               struct address_space *mapping,
+                               struct iov_iter *ii, loff_t pos)
+{
+        struct fuse_conn *fc = get_fuse_conn(mapping->host);
+        unsigned offset = pos & (PAGE_CACHE_SIZE - 1);
+        size_t count = 0;
+        int err;
+
+        req->page_offset = offset;
+
+        do {
+                size_t tmp;
+                struct page *page;
+                pgoff_t index = pos >> PAGE_CACHE_SHIFT;
+                size_t bytes = min_t(size_t, PAGE_CACHE_SIZE - offset,
+                                     iov_iter_count(ii));
+
+                bytes = min_t(size_t, bytes, fc->max_write - count);
+
+ again:
+                err = -EFAULT;
+                if (iov_iter_fault_in_readable(ii, bytes))
+                        break;
+
+                err = -ENOMEM;
+                page = __grab_cache_page(mapping, index);
+                if (!page)
+                        break;
+
+                pagefault_disable();
+                tmp = iov_iter_copy_from_user_atomic(page, ii, offset, bytes);
+                pagefault_enable();
+                flush_dcache_page(page);
+
+                if (!tmp) {
+                        unlock_page(page);
+                        page_cache_release(page);
+                        bytes = min(bytes, iov_iter_single_seg_count(ii));
+                        goto again;
+                }
+
+                err = 0;
+                req->pages[req->num_pages] = page;
+                req->num_pages++;
+
+                iov_iter_advance(ii, tmp);
+                count += tmp;
+                pos += tmp;
+                offset += tmp;
+                if (offset == PAGE_CACHE_SIZE)
+                        offset = 0;
+
+        } while (iov_iter_count(ii) && count < fc->max_write &&
+                 req->num_pages < FUSE_MAX_PAGES_PER_REQ && offset == 0);
+
+        return count > 0 ? count : err;
+}
+
+static ssize_t fuse_perform_write(struct file *file,
+                                  struct address_space *mapping,
+                                  struct iov_iter *ii, loff_t pos)
+{
+        struct inode *inode = mapping->host;
+        struct fuse_conn *fc = get_fuse_conn(inode);
+        int err = 0;
+        ssize_t res = 0;
+
+        if (is_bad_inode(inode))
+                return -EIO;
+
+        do {
+                struct fuse_req *req;
+                ssize_t count;
+
+                req = fuse_get_req(fc);
+                if (IS_ERR(req)) {
+                        err = PTR_ERR(req);
+                        break;
+                }
+
+                count = fuse_fill_write_pages(req, mapping, ii, pos);
+                if (count <= 0) {
+                        err = count;
+                } else {
+                        size_t num_written;
+
+                        num_written = fuse_send_write_pages(req, file, inode,
+                                                            pos, count);
+                        err = req->out.h.error;
+                        if (!err) {
+                                res += num_written;
+                                pos += num_written;
+
+                                /* break out of the loop on short write */
+                                if (num_written != count)
+                                        err = -EIO;
+                        }
+                }
+                fuse_put_request(fc, req);
+        } while (!err && iov_iter_count(ii));
+
+        if (res > 0)
+                fuse_write_update_size(inode, pos);
+
+        fuse_invalidate_attr(inode);
+
+        return res > 0 ? res : err;
+}
+
+static ssize_t fuse_file_aio_write(struct kiocb *iocb, const struct iovec *iov,
+                                   unsigned long nr_segs, loff_t pos)
+{
+        struct file *file = iocb->ki_filp;
+        struct address_space *mapping = file->f_mapping;
+        size_t count = 0;
+        ssize_t written = 0;
+        struct inode *inode = mapping->host;
+        ssize_t err;
+        struct iov_iter i;
+
+        WARN_ON(iocb->ki_pos != pos);
+
+        err = generic_segment_checks(iov, &nr_segs, &count, VERIFY_READ);
+        if (err)
+                return err;
+
+        mutex_lock(&inode->i_mutex);
+        vfs_check_frozen(inode->i_sb, SB_FREEZE_WRITE);
+
+        /* We can write back this queue in page reclaim */
+        current->backing_dev_info = mapping->backing_dev_info;
+
+        err = generic_write_checks(file, &pos, &count, S_ISBLK(inode->i_mode));
+        if (err)
+                goto out;
+
+        if (count == 0)
+                goto out;
+
+        err = remove_suid(file->f_path.dentry);
+        if (err)
+                goto out;
+
+        file_update_time(file);
+
+        iov_iter_init(&i, iov, nr_segs, count, 0);
+        written = fuse_perform_write(file, mapping, &i, pos);
+        if (written >= 0)
+                iocb->ki_pos = pos + written;
+
+out:
+        current->backing_dev_info = NULL;
+        mutex_unlock(&inode->i_mutex);
+
+        return written ? written : err;
+}
+
 static void fuse_release_user_pages(struct fuse_req *req, int write)
 {
         unsigned i;
@@ -1203,7 +1395,7 @@ static const struct file_operations fuse_file_operations = {
         .read           = do_sync_read,
         .aio_read       = fuse_file_aio_read,
         .write          = do_sync_write,
-        .aio_write      = generic_file_aio_write,
+        .aio_write      = fuse_file_aio_write,
         .mmap           = fuse_file_mmap,
         .open           = fuse_open,
         .flush          = fuse_flush,