linux-kernel - [PATCH v21 16/30] ceph: Provide a splice-read stub

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Date:   Sat, 20 May 2023 01:00:35 +0100
From:   David Howells <dhowells@...hat.com>
To:     Jens Axboe <axboe@...nel.dk>, Al Viro <viro@...iv.linux.org.uk>,
        Christoph Hellwig <hch@...radead.org>
Cc:     David Howells <dhowells@...hat.com>,
        Matthew Wilcox <willy@...radead.org>, Jan Kara <jack@...e.cz>,
        Jeff Layton <jlayton@...nel.org>,
        David Hildenbrand <david@...hat.com>,
        Jason Gunthorpe <jgg@...dia.com>,
        Logan Gunthorpe <logang@...tatee.com>,
        Hillf Danton <hdanton@...a.com>,
        Christian Brauner <brauner@...nel.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        linux-fsdevel@...r.kernel.org, linux-block@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        Christoph Hellwig <hch@....de>, Xiubo Li <xiubli@...hat.com>,
        Ilya Dryomov <idryomov@...il.com>, ceph-devel@...r.kernel.org
Subject: [PATCH v21 16/30] ceph: Provide a splice-read stub

Provide a splice_read stub for Ceph.  This does the inode shutdown check
before proceeding and jumps to copy_splice_read() if the file has inline
data or is a synchronous file.

We try and get FILE_RD and either FILE_CACHE and/or FILE_LAZYIO caps and
hold them across filemap_splice_read().  If we fail to get FILE_CACHE or
FILE_LAZYIO capabilities, we use copy_splice_read() instead.

Signed-off-by: David Howells <dhowells@...hat.com>
cc: Christoph Hellwig <hch@....de>
cc: Al Viro <viro@...iv.linux.org.uk>
cc: Jens Axboe <axboe@...nel.dk>
cc: Xiubo Li <xiubli@...hat.com>
cc: Ilya Dryomov <idryomov@...il.com>
cc: Jeff Layton <jlayton@...nel.org>
cc: ceph-devel@...r.kernel.org
cc: linux-fsdevel@...r.kernel.org
cc: linux-block@...r.kernel.org
cc: linux-mm@...ck.org
---

Notes:
    ver #21)
     - Need to drop the caps ref.
     - O_DIRECT is handled by the caller.

 fs/ceph/file.c | 65 +++++++++++++++++++++++++++++++++++++++++++++++++-
 1 file changed, 64 insertions(+), 1 deletion(-)

diff --git a/fs/ceph/file.c b/fs/ceph/file.c
index f4d8bf7dec88..4285f6cb5d3b 100644
--- a/fs/ceph/file.c
+++ b/fs/ceph/file.c
@@ -1745,6 +1745,69 @@ static ssize_t ceph_read_iter(struct kiocb *iocb, struct iov_iter *to)
 	return ret;
 }
 
+/*
+ * Wrap filemap_splice_read with checks for cap bits on the inode.
+ * Atomically grab references, so that those bits are not released
+ * back to the MDS mid-read.
+ */
+static ssize_t ceph_splice_read(struct file *in, loff_t *ppos,
+				struct pipe_inode_info *pipe,
+				size_t len, unsigned int flags)
+{
+	struct ceph_file_info *fi = in->private_data;
+	struct inode *inode = file_inode(in);
+	struct ceph_inode_info *ci = ceph_inode(inode);
+	ssize_t ret;
+	int want = 0, got = 0;
+	CEPH_DEFINE_RW_CONTEXT(rw_ctx, 0);
+
+	dout("splice_read %p %llx.%llx %llu~%zu trying to get caps on %p\n",
+	     inode, ceph_vinop(inode), *ppos, len, inode);
+
+	if (ceph_inode_is_shutdown(inode))
+		return -ESTALE;
+
+	if (ceph_has_inline_data(ci) ||
+	    (fi->flags & CEPH_F_SYNC))
+		return copy_splice_read(in, ppos, pipe, len, flags);
+
+	ceph_start_io_read(inode);
+
+	want = CEPH_CAP_FILE_CACHE;
+	if (fi->fmode & CEPH_FILE_MODE_LAZY)
+		want |= CEPH_CAP_FILE_LAZYIO;
+
+	ret = ceph_get_caps(in, CEPH_CAP_FILE_RD, want, -1, &got);
+	if (ret < 0)
+		goto out_end;
+
+	if ((got & (CEPH_CAP_FILE_CACHE | CEPH_CAP_FILE_LAZYIO)) == 0) {
+		dout("splice_read/sync %p %llx.%llx %llu~%zu got cap refs on %s\n",
+		     inode, ceph_vinop(inode), *ppos, len,
+		     ceph_cap_string(got));
+
+		ceph_put_cap_refs(ci, got);
+		ceph_end_io_read(inode);
+		return copy_splice_read(in, ppos, pipe, len, flags);
+	}
+
+	dout("splice_read %p %llx.%llx %llu~%zu got cap refs on %s\n",
+	     inode, ceph_vinop(inode), *ppos, len, ceph_cap_string(got));
+
+	rw_ctx.caps = got;
+	ceph_add_rw_context(fi, &rw_ctx);
+	ret = filemap_splice_read(in, ppos, pipe, len, flags);
+	ceph_del_rw_context(fi, &rw_ctx);
+
+	dout("splice_read %p %llx.%llx dropping cap refs on %s = %zd\n",
+	     inode, ceph_vinop(inode), ceph_cap_string(got), ret);
+
+	ceph_put_cap_refs(ci, got);
+out_end:
+	ceph_end_io_read(inode);
+	return ret;
+}
+
 /*
  * Take cap references to avoid releasing caps to MDS mid-write.
  *
@@ -2593,7 +2656,7 @@ const struct file_operations ceph_file_fops = {
 	.lock = ceph_lock,
 	.setlease = simple_nosetlease,
 	.flock = ceph_flock,
-	.splice_read = generic_file_splice_read,
+	.splice_read = ceph_splice_read,
 	.splice_write = iter_file_splice_write,
 	.unlocked_ioctl = ceph_ioctl,
 	.compat_ioctl = compat_ptr_ioctl,