The patch implements passing "struct kiocb *async" down the stack up to
fuse_send_read/write where it is used to submit request asynchronously.
async==NULL designates synchronous processing.

Non-trivial part of the patch is changes in fuse_direct_io(): resources
like fuse requests and user pages cannot be released immediately in async
case.

Signed-off-by: Maxim Patlasov <mpatla...@parallels.com>
---
 fs/fuse/cuse.c   |    4 ++--
 fs/fuse/file.c   |   58 ++++++++++++++++++++++++++++++++++++------------------
 fs/fuse/fuse_i.h |    2 +-
 3 files changed, 42 insertions(+), 22 deletions(-)

diff --git a/fs/fuse/cuse.c b/fs/fuse/cuse.c
index 65ce10a..beb99e9 100644
--- a/fs/fuse/cuse.c
+++ b/fs/fuse/cuse.c
@@ -93,7 +93,7 @@ static ssize_t cuse_read(struct file *file, char __user *buf, 
size_t count,
        loff_t pos = 0;
        struct iovec iov = { .iov_base = buf, .iov_len = count };
 
-       return fuse_direct_io(file, &iov, 1, count, &pos, 0);
+       return fuse_direct_io(file, &iov, 1, count, &pos, 0, NULL);
 }
 
 static ssize_t cuse_write(struct file *file, const char __user *buf,
@@ -106,7 +106,7 @@ static ssize_t cuse_write(struct file *file, const char 
__user *buf,
         * No locking or generic_write_checks(), the server is
         * responsible for locking and sanity checks.
         */
-       return fuse_direct_io(file, &iov, 1, count, &pos, 1);
+       return fuse_direct_io(file, &iov, 1, count, &pos, 1, NULL);
 }
 
 static int cuse_open(struct inode *inode, struct file *file)
diff --git a/fs/fuse/file.c b/fs/fuse/file.c
index 634f54a..c585158 100644
--- a/fs/fuse/file.c
+++ b/fs/fuse/file.c
@@ -598,7 +598,8 @@ static size_t fuse_async_req_send(struct fuse_conn *fc, 
struct fuse_req *req,
 }
 
 static size_t fuse_send_read(struct fuse_req *req, struct file *file,
-                            loff_t pos, size_t count, fl_owner_t owner)
+                            loff_t pos, size_t count, fl_owner_t owner,
+                            struct kiocb *async)
 {
        struct fuse_file *ff = file->private_data;
        struct fuse_conn *fc = ff->fc;
@@ -610,6 +611,10 @@ static size_t fuse_send_read(struct fuse_req *req, struct 
file *file,
                inarg->read_flags |= FUSE_READ_LOCKOWNER;
                inarg->lock_owner = fuse_lock_owner_id(fc, owner);
        }
+
+       if (async)
+               return fuse_async_req_send(fc, req, count, async);
+
        fuse_request_send(fc, req);
        return req->out.args[0].size;
 }
@@ -662,7 +667,7 @@ static int fuse_readpage(struct file *file, struct page 
*page)
        req->num_pages = 1;
        req->pages[0] = page;
        req->page_descs[0].length = count;
-       num_read = fuse_send_read(req, file, pos, count, NULL);
+       num_read = fuse_send_read(req, file, pos, count, NULL, NULL);
        err = req->out.h.error;
        fuse_put_request(fc, req);
 
@@ -865,7 +870,8 @@ static void fuse_write_fill(struct fuse_req *req, struct 
fuse_file *ff,
 }
 
 static size_t fuse_send_write(struct fuse_req *req, struct file *file,
-                             loff_t pos, size_t count, fl_owner_t owner)
+                             loff_t pos, size_t count, fl_owner_t owner,
+                             struct kiocb *async)
 {
        struct fuse_file *ff = file->private_data;
        struct fuse_conn *fc = ff->fc;
@@ -877,6 +883,10 @@ static size_t fuse_send_write(struct fuse_req *req, struct 
file *file,
                inarg->write_flags |= FUSE_WRITE_LOCKOWNER;
                inarg->lock_owner = fuse_lock_owner_id(fc, owner);
        }
+
+       if (async)
+               return fuse_async_req_send(fc, req, count, async);
+
        fuse_request_send(fc, req);
        return req->misc.write.out.size;
 }
@@ -904,7 +914,7 @@ static size_t fuse_send_write_pages(struct fuse_req *req, 
struct file *file,
        for (i = 0; i < req->num_pages; i++)
                fuse_wait_on_page_writeback(inode, req->pages[i]->index);
 
-       res = fuse_send_write(req, file, pos, count, NULL);
+       res = fuse_send_write(req, file, pos, count, NULL, NULL);
 
        offset = req->page_descs[0].offset;
        count = res;
@@ -1244,7 +1254,7 @@ static inline int fuse_iter_npages(const struct iov_iter 
*ii_p)
 
 ssize_t fuse_direct_io(struct file *file, const struct iovec *iov,
                       unsigned long nr_segs, size_t count, loff_t *ppos,
-                      int write)
+                      int write, struct kiocb *async)
 {
        struct fuse_file *ff = file->private_data;
        struct fuse_conn *fc = ff->fc;
@@ -1266,16 +1276,22 @@ ssize_t fuse_direct_io(struct file *file, const struct 
iovec *iov,
                size_t nbytes = min(count, nmax);
                int err = fuse_get_user_pages(req, &ii, &nbytes, write);
                if (err) {
+                       if (async)
+                               fuse_put_request(fc, req);
+
                        res = err;
                        break;
                }
 
                if (write)
-                       nres = fuse_send_write(req, file, pos, nbytes, owner);
+                       nres = fuse_send_write(req, file, pos, nbytes, owner,
+                                              async);
                else
-                       nres = fuse_send_read(req, file, pos, nbytes, owner);
+                       nres = fuse_send_read(req, file, pos, nbytes, owner,
+                                             async);
 
-               fuse_release_user_pages(req, !write);
+               if (!async)
+                       fuse_release_user_pages(req, !write);
                if (req->out.h.error) {
                        if (!res)
                                res = req->out.h.error;
@@ -1290,13 +1306,14 @@ ssize_t fuse_direct_io(struct file *file, const struct 
iovec *iov,
                if (nres != nbytes)
                        break;
                if (count) {
-                       fuse_put_request(fc, req);
+                       if (!async)
+                               fuse_put_request(fc, req);
                        req = fuse_get_req(fc, fuse_iter_npages(&ii));
                        if (IS_ERR(req))
                                break;
                }
        }
-       if (!IS_ERR(req))
+       if (!IS_ERR(req) && !async)
                fuse_put_request(fc, req);
        if (res > 0)
                *ppos = pos;
@@ -1306,7 +1323,8 @@ ssize_t fuse_direct_io(struct file *file, const struct 
iovec *iov,
 EXPORT_SYMBOL_GPL(fuse_direct_io);
 
 static ssize_t __fuse_direct_read(struct file *file, const struct iovec *iov,
-                                 unsigned long nr_segs, loff_t *ppos)
+                                 unsigned long nr_segs, loff_t *ppos,
+                                 struct kiocb *async)
 {
        ssize_t res;
        struct inode *inode = file->f_path.dentry->d_inode;
@@ -1315,7 +1333,7 @@ static ssize_t __fuse_direct_read(struct file *file, 
const struct iovec *iov,
                return -EIO;
 
        res = fuse_direct_io(file, iov, nr_segs, iov_length(iov, nr_segs),
-                            ppos, 0);
+                            ppos, 0, async);
 
        fuse_invalidate_attr(inode);
 
@@ -1326,11 +1344,12 @@ static ssize_t fuse_direct_read(struct file *file, char 
__user *buf,
                                     size_t count, loff_t *ppos)
 {
        struct iovec iov = { .iov_base = buf, .iov_len = count };
-       return __fuse_direct_read(file, &iov, 1, ppos);
+       return __fuse_direct_read(file, &iov, 1, ppos, NULL);
 }
 
 static ssize_t __fuse_direct_write(struct file *file, const struct iovec *iov,
-                                  unsigned long nr_segs, loff_t *ppos)
+                                  unsigned long nr_segs, loff_t *ppos,
+                                  struct kiocb *async)
 {
        struct inode *inode = file->f_path.dentry->d_inode;
        size_t count = iov_length(iov, nr_segs);
@@ -1338,8 +1357,9 @@ static ssize_t __fuse_direct_write(struct file *file, 
const struct iovec *iov,
 
        res = generic_write_checks(file, ppos, &count, 0);
        if (!res) {
-               res = fuse_direct_io(file, iov, nr_segs, count, ppos, 1);
-               if (res > 0)
+               res = fuse_direct_io(file, iov, nr_segs, count, ppos, 1,
+                                    async);
+               if (!async && res > 0)
                        fuse_write_update_size(inode, *ppos);
        }
 
@@ -1360,7 +1380,7 @@ static ssize_t fuse_direct_write(struct file *file, const 
char __user *buf,
 
        /* Don't allow parallel writes to the same file */
        mutex_lock(&inode->i_mutex);
-       res = __fuse_direct_write(file, &iov, 1, ppos);
+       res = __fuse_direct_write(file, &iov, 1, ppos, NULL);
        mutex_unlock(&inode->i_mutex);
 
        return res;
@@ -2333,9 +2353,9 @@ fuse_direct_IO(int rw, struct kiocb *iocb, const struct 
iovec *iov,
        pos = offset;
 
        if (rw == WRITE)
-               ret = __fuse_direct_write(file, iov, nr_segs, &pos);
+               ret = __fuse_direct_write(file, iov, nr_segs, &pos, NULL);
        else
-               ret = __fuse_direct_read(file, iov, nr_segs, &pos);
+               ret = __fuse_direct_read(file, iov, nr_segs, &pos, NULL);
 
        return ret;
 }
diff --git a/fs/fuse/fuse_i.h b/fs/fuse/fuse_i.h
index 618d48a..173c959 100644
--- a/fs/fuse/fuse_i.h
+++ b/fs/fuse/fuse_i.h
@@ -828,7 +828,7 @@ int fuse_do_open(struct fuse_conn *fc, u64 nodeid, struct 
file *file,
                 bool isdir);
 ssize_t fuse_direct_io(struct file *file, const struct iovec *iov,
                       unsigned long nr_segs, size_t count, loff_t *ppos,
-                      int write);
+                      int write, struct kiocb *async);
 long fuse_do_ioctl(struct file *file, unsigned int cmd, unsigned long arg,
                   unsigned int flags);
 long fuse_ioctl_common(struct file *file, unsigned int cmd,

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