[PATCH v4 30/39] netfs: Implement buffered write API

David Howells
2023-12-13T15:26:14Z

Institute a netfs write helper, netfs_file_write_iter(), to be pointed at
by the network filesystem ->write_iter() call. Make it handled buffered
writes by calling the previously defined netfs_perform_write() to copy the
source data into the pagecache.

Signed-off-by: David Howells <dhowells@redhat.com>
cc: Jeff Layton <jlayton@kernel.org>
cc: linux-cachefs@redhat.com
cc: linux-fsdevel@vger.kernel.org
cc: linux-mm@kvack.org
---
fs/netfs/buffered_write.c | 83 +++++++++++++++++++++++++++++++++++++++
include/linux/netfs.h | 3 ++
2 files changed, 86 insertions(+)

diff --git a/fs/netfs/buffered_write.c b/fs/netfs/buffered_write.c
index b76688e98f81..f244123ab568 100644
--- a/fs/netfs/buffered_write.c
+++ b/fs/netfs/buffered_write.c
@@ -333,3 +333,86 @@ ssize_t netfs_perform_write(struct kiocb *iocb, struct iov_iter *iter,
goto out;
}
EXPORT_SYMBOL(netfs_perform_write);
+
+/**
+ * netfs_buffered_write_iter_locked - write data to a file
+ * @iocb: IO state structure (file, offset, etc.)
+ * @from: iov_iter with data to write
+ * @netfs_group: Grouping for dirty pages (eg. ceph snaps).
+ *
+ * This function does all the work needed for actually writing data to a
+ * file. It does all basic checks, removes SUID from the file, updates
+ * modification times and calls proper subroutines depending on whether we
+ * do direct IO or a standard buffered write.
+ *
+ * The caller must hold appropriate locks around this function and have called
+ * generic_write_checks() already. The caller is also responsible for doing
+ * any necessary syncing afterwards.
+ *
+ * This function does *not* take care of syncing data in case of O_SYNC write.
+ * A caller has to handle it. This is mainly due to the fact that we want to
+ * avoid syncing under i_rwsem.
+ *
+ * Return:
+ * * number of bytes written, even for truncated writes
+ * * negative error code if no data has been written at all
+ */
+ssize_t netfs_buffered_write_iter_locked(struct kiocb *iocb, struct iov_iter *from,
+ struct netfs_group *netfs_group)
+{
+ struct file *file = iocb->ki_filp;
+ ssize_t ret;
+
+ trace_netfs_write_iter(iocb, from);
+
+ ret = file_remove_privs(file);
+ if (ret)
+ return ret;
+
+ ret = file_update_time(file);
+ if (ret)
+ return ret;
+
+ return netfs_perform_write(iocb, from, netfs_group);
+}
+EXPORT_SYMBOL(netfs_buffered_write_iter_locked);
+
+/**
+ * netfs_file_write_iter - write data to a file
+ * @iocb: IO state structure
+ * @from: iov_iter with data to write
+ *
+ * Perform a write to a file, writing into the pagecache if possible and doing
+ * an unbuffered write instead if not.
+ *
+ * Return:
+ * * Negative error code if no data has been written at all of
+ * vfs_fsync_range() failed for a synchronous write
+ * * Number of bytes written, even for truncated writes
+ */
+ssize_t netfs_file_write_iter(struct kiocb *iocb, struct iov_iter *from)
+{
+ struct file *file = iocb->ki_filp;
+ struct inode *inode = file->f_mapping->host;
+ struct netfs_inode *ictx = netfs_inode(inode);
+ ssize_t ret;
+
+ _enter("%llx,%zx,%llx", iocb->ki_pos, iov_iter_count(from), i_size_read(inode));
+
+ if ((iocb->ki_flags & IOCB_DIRECT) ||
+ test_bit(NETFS_ICTX_UNBUFFERED, &ictx->flags))
+ return netfs_unbuffered_write_iter(iocb, from);
+
+ ret = netfs_start_io_write(inode);
+ if (ret < 0)
+ return ret;
+
+ ret = generic_write_checks(iocb, from);
+ if (ret > 0)
+ ret = netfs_buffered_write_iter_locked(iocb, from, NULL);
+ netfs_end_io_write(inode);
+ if (ret > 0)
+ ret = generic_write_sync(iocb, ret);
+ return ret;
+}
+EXPORT_SYMBOL(netfs_file_write_iter);
diff --git a/include/linux/netfs.h b/include/linux/netfs.h
index 00c87f4e809c..702b864a4993 100644
--- a/include/linux/netfs.h
+++ b/include/linux/netfs.h
@@ -385,7 +385,10 @@ ssize_t netfs_unbuffered_read_iter(struct kiocb *iocb, struct iov_iter *iter);
/* High-level write API */
ssize_t netfs_perform_write(struct kiocb *iocb, struct iov_iter *iter,
struct netfs_group *netfs_group);
+ssize_t netfs_buffered_write_iter_locked(struct kiocb *iocb, struct iov_iter *from,
+ struct netfs_group *netfs_group);
ssize_t netfs_unbuffered_write_iter(struct kiocb *iocb, struct iov_iter *from);
+ssize_t netfs_file_write_iter(struct kiocb *iocb, struct iov_iter *from);

/* Address operations API */
struct readahead_control;