[PATCH 2/4] fuse: re-work fuse_get_user_pages() to operate on iovec[]

[Maxim Patlasov <mpatlasov@parallels.com>]

Now fuse_get_user_pages() takes iovec[] as argument and packs so much data
from it to req->pages[] as possible.

Signed-off-by: Maxim Patlasov <mpatlasov@parallels.com>
---
 fs/fuse/file.c |   64 +++++++++++++++++++++++++++++++++++++++++---------------
 1 files changed, 47 insertions(+), 17 deletions(-)

diff --git a/fs/fuse/file.c b/fs/fuse/file.c
index b321a68..d84416d 100644
--- a/fs/fuse/file.c
+++ b/fs/fuse/file.c
@@ -1020,41 +1020,71 @@ static void fuse_release_user_pages(struct fuse_req *req, int write)
 	}
 }
 
-static int fuse_get_user_pages(struct fuse_req *req, const char __user *buf,
+static int fuse_get_user_pages(struct fuse_req *req,
+			       const struct iovec **iov_pp,
+			       unsigned long *nr_segs_p,
+			       size_t *iov_offset_p,
 			       size_t *nbytesp, int write)
 {
-	size_t nbytes = *nbytesp;
-	unsigned long user_addr = (unsigned long) buf;
-	unsigned offset = user_addr & ~PAGE_MASK;
-	int npages;
+	size_t nbytes = 0;  /* # bytes already packed in req */
 
 	/* Special case for kernel I/O: can copy directly into the buffer */
 	if (segment_eq(get_fs(), KERNEL_DS)) {
+		BUG_ON(*iov_offset_p);
 		if (write)
-			req->in.args[1].value = (void *) user_addr;
+			req->in.args[1].value = (*iov_pp)->iov_base;
 		else
-			req->out.args[0].value = (void *) user_addr;
+			req->out.args[0].value = (*iov_pp)->iov_base;
 
+		(*iov_pp)++;
+		(*nr_segs_p)--;
 		return 0;
 	}
 
-	nbytes = min_t(size_t, nbytes, FUSE_MAX_PAGES_PER_REQ << PAGE_SHIFT);
-	npages = (nbytes + offset + PAGE_SIZE - 1) >> PAGE_SHIFT;
-	npages = clamp(npages, 1, FUSE_MAX_PAGES_PER_REQ);
-	npages = get_user_pages_fast(user_addr, npages, !write, req->pages);
-	if (npages < 0)
-		return npages;
+	req->iovec = *iov_pp;
+	req->iov_offset = *iov_offset_p;
 
-	req->num_pages = npages;
-	req->page_offset = offset;
+	while (nbytes < *nbytesp && req->num_pages < FUSE_MAX_PAGES_PER_REQ) {
+		int npages;
+		unsigned long user_addr = (unsigned long)(*iov_pp)->iov_base +
+					  *iov_offset_p;
+		unsigned offset = user_addr & ~PAGE_MASK;
+		size_t frag_size = min_t(size_t,
+					 (*iov_pp)->iov_len - *iov_offset_p,
+					 *nbytesp - nbytes);
+
+		int n = FUSE_MAX_PAGES_PER_REQ - req->num_pages;
+		frag_size = min_t(size_t, frag_size, n << PAGE_SHIFT);
+
+		npages = (frag_size + offset + PAGE_SIZE - 1) >> PAGE_SHIFT;
+		npages = clamp(npages, 1, n);
+
+		npages = get_user_pages_fast(user_addr, npages, !write,
+					     &req->pages[req->num_pages]);
+		if (npages < 0)
+			return npages;
+
+		frag_size = min_t(size_t, frag_size,
+				  (npages << PAGE_SHIFT) - offset);
+		nbytes += frag_size;
+
+		if (frag_size < (*iov_pp)->iov_len - *iov_offset_p) {
+			*iov_offset_p += frag_size;
+		} else {
+			(*iov_pp)++;
+			(*nr_segs_p)--;
+			*iov_offset_p = 0;
+		}
+
+		req->num_pages += npages;
+	}
 
 	if (write)
 		req->in.argpages = 1;
 	else
 		req->out.argpages = 1;
 
-	nbytes = (req->num_pages << PAGE_SHIFT) - req->page_offset;
-	*nbytesp = min(*nbytesp, nbytes);
+	*nbytesp = nbytes;
 
 	return 0;
 }