fuse: add retrieve request

Userspace filesystem can request data to be retrieved from the inode's
mapping.  This request is synchronous and the retrieved data is queued
as a new request.  If the write to the fuse device returns an error
then the retrieve request was not completed and a reply will not be
sent.

Only present pages are returned in the retrieve reply.  Retrieving
stops when it finds a non-present page and only data prior to that is
returned.

This request doesn't change the dirty state of pages.

Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>

3 files changed, 152 insertions, 1 deletions

diff --git a/fs/fuse/dev.c b/fs/fuse/dev.c
index 8e01c865586e..69ad053ffd78 100644
--- a/fs/fuse/dev.c
+++ b/fs/fuse/dev.c
@@ -239,7 +239,6 @@ static u64 fuse_get_unique(struct fuse_conn *fc)
 
 static void queue_request(struct fuse_conn *fc, struct fuse_req *req)
 {
-        req->in.h.unique = fuse_get_unique(fc);
         req->in.h.len = sizeof(struct fuse_in_header) +
                 len_args(req->in.numargs, (struct fuse_arg *) req->in.args);
         list_add_tail(&req->list, &fc->pending);
@@ -261,6 +260,7 @@ static void flush_bg_queue(struct fuse_conn *fc)
                 req = list_entry(fc->bg_queue.next, struct fuse_req, list);
                 list_del(&req->list);
                 fc->active_background++;
+                req->in.h.unique = fuse_get_unique(fc);
                 queue_request(fc, req);
         }
 }
@@ -398,6 +398,7 @@ void fuse_request_send(struct fuse_conn *fc, struct fuse_req *req)
         else if (fc->conn_error)
                 req->out.h.error = -ECONNREFUSED;
         else {
+                req->in.h.unique = fuse_get_unique(fc);
                 queue_request(fc, req);
                 /* acquire extra reference, since request is still needed
                    after request_end() */
@@ -450,6 +451,23 @@ void fuse_request_send_background(struct fuse_conn *fc, struct fuse_req *req)
 }
 EXPORT_SYMBOL_GPL(fuse_request_send_background);
 
+static int fuse_request_send_notify_reply(struct fuse_conn *fc,
+                                          struct fuse_req *req, u64 unique)
+{
+        int err = -ENODEV;
+
+        req->isreply = 0;
+        req->in.h.unique = unique;
+        spin_lock(&fc->lock);
+        if (fc->connected) {
+                queue_request(fc, req);
+                err = 0;
+        }
+        spin_unlock(&fc->lock);
+
+        return err;
+}
+
 /*
  * Called under fc->lock
  *
@@ -1316,6 +1334,114 @@ out_finish:
         return err;
 }
 
+static void fuse_retrieve_end(struct fuse_conn *fc, struct fuse_req *req)
+{
+        int i;
+
+        for (i = 0; i < req->num_pages; i++) {
+                struct page *page = req->pages[i];
+                page_cache_release(page);
+        }
+}
+
+static int fuse_retrieve(struct fuse_conn *fc, struct inode *inode,
+                         struct fuse_notify_retrieve_out *outarg)
+{
+        int err;
+        struct address_space *mapping = inode->i_mapping;
+        struct fuse_req *req;
+        pgoff_t index;
+        loff_t file_size;
+        unsigned int num;
+        unsigned int offset;
+        size_t total_len;
+
+        req = fuse_get_req(fc);
+        if (IS_ERR(req))
+                return PTR_ERR(req);
+
+        offset = outarg->offset & ~PAGE_CACHE_MASK;
+
+        req->in.h.opcode = FUSE_NOTIFY_REPLY;
+        req->in.h.nodeid = outarg->nodeid;
+        req->in.numargs = 2;
+        req->in.argpages = 1;
+        req->page_offset = offset;
+        req->end = fuse_retrieve_end;
+
+        index = outarg->offset >> PAGE_CACHE_SHIFT;
+        file_size = i_size_read(inode);
+        num = outarg->size;
+        if (outarg->offset > file_size)
+                num = 0;
+        else if (outarg->offset + num > file_size)
+                num = file_size - outarg->offset;
+
+        while (num) {
+                struct page *page;
+                unsigned int this_num;
+
+                page = find_get_page(mapping, index);
+                if (!page)
+                        break;
+
+                this_num = min_t(unsigned, num, PAGE_CACHE_SIZE - offset);
+                req->pages[req->num_pages] = page;
+                req->num_pages++;
+
+                num -= this_num;
+                total_len += this_num;
+        }
+        req->misc.retrieve_in.offset = outarg->offset;
+        req->misc.retrieve_in.size = total_len;
+        req->in.args[0].size = sizeof(req->misc.retrieve_in);
+        req->in.args[0].value = &req->misc.retrieve_in;
+        req->in.args[1].size = total_len;
+
+        err = fuse_request_send_notify_reply(fc, req, outarg->notify_unique);
+        if (err)
+                fuse_retrieve_end(fc, req);
+
+        return err;
+}
+
+static int fuse_notify_retrieve(struct fuse_conn *fc, unsigned int size,
+                                struct fuse_copy_state *cs)
+{
+        struct fuse_notify_retrieve_out outarg;
+        struct inode *inode;
+        int err;
+
+        err = -EINVAL;
+        if (size != sizeof(outarg))
+                goto copy_finish;
+
+        err = fuse_copy_one(cs, &outarg, sizeof(outarg));
+        if (err)
+                goto copy_finish;
+
+        fuse_copy_finish(cs);
+
+        down_read(&fc->killsb);
+        err = -ENOENT;
+        if (fc->sb) {
+                u64 nodeid = outarg.nodeid;
+
+                inode = ilookup5(fc->sb, nodeid, fuse_inode_eq, &nodeid);
+                if (inode) {
+                        err = fuse_retrieve(fc, inode, &outarg);
+                        iput(inode);
+                }
+        }
+        up_read(&fc->killsb);
+
+        return err;
+
+copy_finish:
+        fuse_copy_finish(cs);
+        return err;
+}
+
 static int fuse_notify(struct fuse_conn *fc, enum fuse_notify_code code,
                        unsigned int size, struct fuse_copy_state *cs)
 {
@@ -1332,6 +1458,9 @@ static int fuse_notify(struct fuse_conn *fc, enum fuse_notify_code code,
         case FUSE_NOTIFY_STORE:
                 return fuse_notify_store(fc, size, cs);
 
+        case FUSE_NOTIFY_RETRIEVE:
+                return fuse_notify_retrieve(fc, size, cs);
+
         default:
                 fuse_copy_finish(cs);
                 return -EINVAL;
diff --git a/fs/fuse/fuse_i.h b/fs/fuse/fuse_i.h
index 61267d8d527b..57d4a3a0f102 100644
--- a/fs/fuse/fuse_i.h
+++ b/fs/fuse/fuse_i.h
@@ -272,6 +272,7 @@ struct fuse_req {
                         struct fuse_write_in in;
                         struct fuse_write_out out;
                 } write;
+                struct fuse_notify_retrieve_in retrieve_in;
                 struct fuse_lk_in lk_in;
         } misc;
 
diff --git a/include/linux/fuse.h b/include/linux/fuse.h
index a90bd49834aa..c3c578e09833 100644
--- a/include/linux/fuse.h
+++ b/include/linux/fuse.h
@@ -40,6 +40,7 @@
  *
  * 7.15
  *  - add store notify
+ *  - add retrieve notify
  */
 
 #ifndef _LINUX_FUSE_H
@@ -254,6 +255,7 @@ enum fuse_opcode {
         FUSE_DESTROY       = 38,
         FUSE_IOCTL         = 39,
         FUSE_POLL          = 40,
+        FUSE_NOTIFY_REPLY  = 41,
 
         /* CUSE specific operations */
         CUSE_INIT          = 4096,
@@ -264,6 +266,7 @@ enum fuse_notify_code {
         FUSE_NOTIFY_INVAL_INODE = 2,
         FUSE_NOTIFY_INVAL_ENTRY = 3,
         FUSE_NOTIFY_STORE = 4,
+        FUSE_NOTIFY_RETRIEVE = 5,
         FUSE_NOTIFY_CODE_MAX,
 };
 
@@ -579,4 +582,22 @@ struct fuse_notify_store_out {
         __u32   padding;
 };
 
+struct fuse_notify_retrieve_out {
+        __u64   notify_unique;
+        __u64   nodeid;
+        __u64   offset;
+        __u32   size;
+        __u32   padding;
+};
+
+/* Matches the size of fuse_write_in */
+struct fuse_notify_retrieve_in {
+        __u64   dummy1;
+        __u64   offset;
+        __u32   size;
+        __u32   dummy2;
+        __u64   dummy3;
+        __u64   dummy4;
+};
+
 #endif /* _LINUX_FUSE_H */