[PATCH 1/6] fuse: general infrastructure for pages[] of variable size

[Maxim Patlasov <mpatlasov@parallels.com>]

The patch removes inline array of FUSE_MAX_PAGES_PER_REQ page pointers from
fuse_req. Instead of that, req->pages may now point either to small inline
array or to an array allocated dynamically.

This essentially means that all callers of fuse_request_alloc[_nofs] should
pass the number of pages needed explicitly.

The patch doesn't make any logic changes.
---
 fs/fuse/dev.c    |   40 ++++++++++++++++++++++++++++++----------
 fs/fuse/file.c   |    4 ++--
 fs/fuse/fuse_i.h |    9 ++++++---
 fs/fuse/inode.c  |    4 ++--
 4 files changed, 40 insertions(+), 17 deletions(-)

diff --git a/fs/fuse/dev.c b/fs/fuse/dev.c
index 7df2b5e..c0283a1 100644
--- a/fs/fuse/dev.c
+++ b/fs/fuse/dev.c
@@ -36,32 +36,52 @@ static struct fuse_conn *fuse_get_conn(struct file *file)
 
 static void fuse_request_init(struct fuse_req *req)
 {
+	struct page **pages = req->pages;
+
 	memset(req, 0, sizeof(*req));
 	INIT_LIST_HEAD(&req->list);
 	INIT_LIST_HEAD(&req->intr_entry);
 	init_waitqueue_head(&req->waitq);
 	atomic_set(&req->count, 1);
+
+	req->pages = pages;
 }
 
-struct fuse_req *fuse_request_alloc(void)
+static struct fuse_req *__fuse_request_alloc(int npages, gfp_t flags)
 {
-	struct fuse_req *req = kmem_cache_alloc(fuse_req_cachep, GFP_KERNEL);
-	if (req)
+	struct fuse_req *req = kmem_cache_alloc(fuse_req_cachep, flags);
+	if (req) {
+		if (npages <= 1)
+			req->pages = req->inline_pages;
+		else
+			req->pages = kmalloc(sizeof(struct page *) * npages,
+					     flags);
+
+		if (!req->pages) {
+			kmem_cache_free(fuse_req_cachep, req);
+			return NULL;
+		}
+
 		fuse_request_init(req);
+	}
 	return req;
 }
+
+struct fuse_req *fuse_request_alloc(int npages)
+{
+	return __fuse_request_alloc(npages, GFP_KERNEL);
+}
 EXPORT_SYMBOL_GPL(fuse_request_alloc);
 
-struct fuse_req *fuse_request_alloc_nofs(void)
+struct fuse_req *fuse_request_alloc_nofs(int npages)
 {
-	struct fuse_req *req = kmem_cache_alloc(fuse_req_cachep, GFP_NOFS);
-	if (req)
-		fuse_request_init(req);
-	return req;
+	return __fuse_request_alloc(npages, GFP_NOFS);
 }
 
 void fuse_request_free(struct fuse_req *req)
 {
+	if (req->pages != req->inline_pages)
+		kfree(req->pages);
 	kmem_cache_free(fuse_req_cachep, req);
 }
 
@@ -116,7 +136,7 @@ struct fuse_req *fuse_get_req(struct fuse_conn *fc)
 	if (!fc->connected)
 		goto out;
 
-	req = fuse_request_alloc();
+	req = fuse_request_alloc(FUSE_MAX_PAGES_PER_REQ);
 	err = -ENOMEM;
 	if (!req)
 		goto out;
@@ -193,7 +213,7 @@ struct fuse_req *fuse_get_req_nofail(struct fuse_conn *fc, struct file *file)
 
 	atomic_inc(&fc->num_waiting);
 	wait_event(fc->blocked_waitq, !fc->blocked);
-	req = fuse_request_alloc();
+	req = fuse_request_alloc(FUSE_MAX_PAGES_PER_REQ);
 	if (!req)
 		req = get_reserved_req(fc, file);
 
diff --git a/fs/fuse/file.c b/fs/fuse/file.c
index aba15f1..7423ea4 100644
--- a/fs/fuse/file.c
+++ b/fs/fuse/file.c
@@ -57,7 +57,7 @@ struct fuse_file *fuse_file_alloc(struct fuse_conn *fc)
 		return NULL;
 
 	ff->fc = fc;
-	ff->reserved_req = fuse_request_alloc();
+	ff->reserved_req = fuse_request_alloc(0);
 	if (unlikely(!ff->reserved_req)) {
 		kfree(ff);
 		return NULL;
@@ -1272,7 +1272,7 @@ static int fuse_writepage_locked(struct page *page)
 
 	set_page_writeback(page);
 
-	req = fuse_request_alloc_nofs();
+	req = fuse_request_alloc_nofs(1);
 	if (!req)
 		goto err;
 
diff --git a/fs/fuse/fuse_i.h b/fs/fuse/fuse_i.h
index e24dd74..5e78840 100644
--- a/fs/fuse/fuse_i.h
+++ b/fs/fuse/fuse_i.h
@@ -291,7 +291,10 @@ struct fuse_req {
 	} misc;
 
 	/** page vector */
-	struct page *pages[FUSE_MAX_PAGES_PER_REQ];
+	struct page **pages;
+
+	/** inline page vector */
+	struct page *inline_pages[1];
 
 	/** number of pages in vector */
 	unsigned num_pages;
@@ -658,9 +661,9 @@ void fuse_ctl_cleanup(void);
 /**
  * Allocate a request
  */
-struct fuse_req *fuse_request_alloc(void);
+struct fuse_req *fuse_request_alloc(int npages);
 
-struct fuse_req *fuse_request_alloc_nofs(void);
+struct fuse_req *fuse_request_alloc_nofs(int npages);
 
 /**
  * Free a request
diff --git a/fs/fuse/inode.c b/fs/fuse/inode.c
index ce0a283..3f399ba 100644
--- a/fs/fuse/inode.c
+++ b/fs/fuse/inode.c
@@ -1027,12 +1027,12 @@ static int fuse_fill_super(struct super_block *sb, void *data, int silent)
 	/* only now - we want root dentry with NULL ->d_op */
 	sb->s_d_op = &fuse_dentry_operations;
 
-	init_req = fuse_request_alloc();
+	init_req = fuse_request_alloc(0);
 	if (!init_req)
 		goto err_put_root;
 
 	if (is_bdev) {
-		fc->destroy_req = fuse_request_alloc();
+		fc->destroy_req = fuse_request_alloc(0);
 		if (!fc->destroy_req)
 			goto err_free_init_req;
 	}