fuse: O_DIRECT support for files

Implement ->direct_IO() method in aops. The ->direct_IO() method combines
the existing fuse_direct_read/fuse_direct_write methods to implement
O_DIRECT functionality.

Reaching ->direct_IO() in the read path via generic_file_aio_read ensures
proper synchronization with page cache with its existing framework.

Reaching ->direct_IO() in the write path via fuse_file_aio_write is made
to come via generic_file_direct_write() which makes it play nice with
the page cache w.r.t other mmap pages etc.

On files marked 'direct_io' by the filesystem server, IO always follows
the fuse_direct_read/write path. There is no effect of fcntl(O_DIRECT)
and it always succeeds.

On files not marked with 'direct_io' by the filesystem server, the IO
path depends on O_DIRECT flag by the application. This can be passed
at the time of open() as well as via fcntl().

Note that asynchronous O_DIRECT iocb jobs are completed synchronously
always (this has been the case with FUSE even before this patch)

Signed-off-by: Anand Avati <avati@redhat.com>
Reviewed-by: Jeff Moyer <jmoyer@redhat.com>
Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>

2 files changed, 112 insertions, 20 deletions

diff --git a/fs/fuse/dir.c b/fs/fuse/dir.c
index da379070fab5..df5ac048dc74 100644
--- a/fs/fuse/dir.c
+++ b/fs/fuse/dir.c
@@ -387,9 +387,6 @@ static int fuse_create_open(struct inode *dir, struct dentry *entry,
         if (fc->no_create)
                 return -ENOSYS;
 
-        if (flags & O_DIRECT)
-                return -EINVAL;
-
         forget = fuse_alloc_forget();
         if (!forget)
                 return -ENOMEM;
diff --git a/fs/fuse/file.c b/fs/fuse/file.c
index 4a199fd93fbd..8ca007d09c96 100644
--- a/fs/fuse/file.c
+++ b/fs/fuse/file.c
@@ -194,10 +194,6 @@ int fuse_open_common(struct inode *inode, struct file *file, bool isdir)
         struct fuse_conn *fc = get_fuse_conn(inode);
         int err;
 
-        /* VFS checks this, but only _after_ ->open() */
-        if (file->f_flags & O_DIRECT)
-                return -EINVAL;
-
         err = generic_file_open(inode, file);
         if (err)
                 return err;
@@ -932,17 +928,23 @@ static ssize_t fuse_file_aio_write(struct kiocb *iocb, const struct iovec *iov,
         struct file *file = iocb->ki_filp;
         struct address_space *mapping = file->f_mapping;
         size_t count = 0;
+        size_t ocount = 0;
         ssize_t written = 0;
+        ssize_t written_buffered = 0;
         struct inode *inode = mapping->host;
         ssize_t err;
         struct iov_iter i;
+        loff_t endbyte = 0;
 
         WARN_ON(iocb->ki_pos != pos);
 
-        err = generic_segment_checks(iov, &nr_segs, &count, VERIFY_READ);
+        ocount = 0;
+        err = generic_segment_checks(iov, &nr_segs, &ocount, VERIFY_READ);
         if (err)
                 return err;
 
+        count = ocount;
+
         mutex_lock(&inode->i_mutex);
         vfs_check_frozen(inode->i_sb, SB_FREEZE_WRITE);
 
@@ -962,11 +964,41 @@ static ssize_t fuse_file_aio_write(struct kiocb *iocb, const struct iovec *iov,
 
         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;
+        if (file->f_flags & O_DIRECT) {
+                written = generic_file_direct_write(iocb, iov, &nr_segs,
+                                                    pos, &iocb->ki_pos,
+                                                    count, ocount);
+                if (written < 0 || written == count)
+                        goto out;
+
+                pos += written;
+                count -= written;
 
+                iov_iter_init(&i, iov, nr_segs, count, written);
+                written_buffered = fuse_perform_write(file, mapping, &i, pos);
+                if (written_buffered < 0) {
+                        err = written_buffered;
+                        goto out;
+                }
+                endbyte = pos + written_buffered - 1;
+
+                err = filemap_write_and_wait_range(file->f_mapping, pos,
+                                                   endbyte);
+                if (err)
+                        goto out;
+
+                invalidate_mapping_pages(file->f_mapping,
+                                         pos >> PAGE_CACHE_SHIFT,
+                                         endbyte >> PAGE_CACHE_SHIFT);
+
+                written += written_buffered;
+                iocb->ki_pos = pos + written_buffered;
+        } else {
+                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);
@@ -1101,30 +1133,41 @@ static ssize_t fuse_direct_read(struct file *file, char __user *buf,
         return res;
 }
 
-static ssize_t fuse_direct_write(struct file *file, const char __user *buf,
-                                 size_t count, loff_t *ppos)
+static ssize_t __fuse_direct_write(struct file *file, const char __user *buf,
+                                   size_t count, loff_t *ppos)
 {
         struct inode *inode = file->f_path.dentry->d_inode;
         ssize_t res;
 
-        if (is_bad_inode(inode))
-                return -EIO;
-
-        /* Don't allow parallel writes to the same file */
-        mutex_lock(&inode->i_mutex);
         res = generic_write_checks(file, ppos, &count, 0);
         if (!res) {
                 res = fuse_direct_io(file, buf, count, ppos, 1);
                 if (res > 0)
                         fuse_write_update_size(inode, *ppos);
         }
-        mutex_unlock(&inode->i_mutex);
 
         fuse_invalidate_attr(inode);
 
         return res;
 }
 
+static ssize_t fuse_direct_write(struct file *file, const char __user *buf,
+                                 size_t count, loff_t *ppos)
+{
+        struct inode *inode = file->f_path.dentry->d_inode;
+        ssize_t res;
+
+        if (is_bad_inode(inode))
+                return -EIO;
+
+        /* Don't allow parallel writes to the same file */
+        mutex_lock(&inode->i_mutex);
+        res = __fuse_direct_write(file, buf, count, ppos);
+        mutex_unlock(&inode->i_mutex);
+
+        return res;
+}
+
 static void fuse_writepage_free(struct fuse_conn *fc, struct fuse_req *req)
 {
         __free_page(req->pages[0]);
@@ -2077,6 +2120,57 @@ int fuse_notify_poll_wakeup(struct fuse_conn *fc,
         return 0;
 }
 
+static ssize_t fuse_loop_dio(struct file *filp, const struct iovec *iov,
+                             unsigned long nr_segs, loff_t *ppos, int rw)
+{
+        const struct iovec *vector = iov;
+        ssize_t ret = 0;
+
+        while (nr_segs > 0) {
+                void __user *base;
+                size_t len;
+                ssize_t nr;
+
+                base = vector->iov_base;
+                len = vector->iov_len;
+                vector++;
+                nr_segs--;
+
+                if (rw == WRITE)
+                        nr = __fuse_direct_write(filp, base, len, ppos);
+                else
+                        nr = fuse_direct_read(filp, base, len, ppos);
+
+                if (nr < 0) {
+                        if (!ret)
+                                ret = nr;
+                        break;
+                }
+                ret += nr;
+                if (nr != len)
+                        break;
+        }
+
+        return ret;
+}
+
+
+static ssize_t
+fuse_direct_IO(int rw, struct kiocb *iocb, const struct iovec *iov,
+                        loff_t offset, unsigned long nr_segs)
+{
+        ssize_t ret = 0;
+        struct file *file = NULL;
+        loff_t pos = 0;
+
+        file = iocb->ki_filp;
+        pos = offset;
+
+        ret = fuse_loop_dio(file, iov, nr_segs, &pos, rw);
+
+        return ret;
+}
+
 static const struct file_operations fuse_file_operations = {
         .llseek         = fuse_file_llseek,
         .read           = do_sync_read,
@@ -2120,6 +2214,7 @@ static const struct address_space_operations fuse_file_aops  = {
         .readpages      = fuse_readpages,
         .set_page_dirty = __set_page_dirty_nobuffers,
         .bmap           = fuse_bmap,
+        .direct_IO      = fuse_direct_IO,
 };
 
 void fuse_init_file_inode(struct inode *inode)