On Fri, Feb 8, 2019 at 6:34 PM Jens Axboe [off-list ref] wrote:

From: Christoph Hellwig <hch@lst.de>

Add a new fsync opcode, which either syncs a range if one is passed,
or the whole file if the offset and length fields are both cleared
to zero.  A flag is provided to use fdatasync semantics, that is only
force out metadata which is required to retrieve the file data, but
not others like metadata.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
---

[...]

+static int io_fsync(struct io_kiocb *req, const struct io_uring_sqe *sqe,
+                   bool force_nonblock)
+{
+       struct io_ring_ctx *ctx = req->ctx;
+       loff_t sqe_off = READ_ONCE(sqe->off);
+       loff_t sqe_len = READ_ONCE(sqe->len);
+       loff_t end = sqe_off + sqe_len;
+       unsigned fsync_flags;
+       struct file *file;
+       int ret, fd;
+
+       /* fsync always requires a blocking context */
+       if (force_nonblock)
+               return -EAGAIN;
+
+       if (unlikely(sqe->addr || sqe->ioprio))
+               return -EINVAL;
+
+       fsync_flags = READ_ONCE(sqe->fsync_flags);
+       if (unlikely(fsync_flags & ~IORING_FSYNC_DATASYNC))
+               return -EINVAL;
+
+       fd = READ_ONCE(sqe->fd);
+       file = fget(fd);

This always runs on the workqueue, right? Is it possible to call
fget() on a workqueue?

+       if (unlikely(!file))
+               return -EBADF;
+
+       ret = vfs_fsync_range(file, sqe_off, end > 0 ? end : LLONG_MAX,
+                               fsync_flags & IORING_FSYNC_DATASYNC);
+
+       fput(file);
+       io_cqring_add_event(ctx, sqe->user_data, ret, 0);
+       io_free_req(req);
+       return 0;
+}

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