+// SPDX-License-Identifier: GPL-2.0
+/*
+ * FUSE inode io modes.
+ *
+ * Copyright (c) 2024 CTERA Networks.
+ */
+
+#include "fuse_i.h"
+
+#include <linux/kernel.h>
+#include <linux/sched.h>
+#include <linux/file.h>
+#include <linux/fs.h>
+
+/*
+ * Start cached io mode, where parallel dio writes are not allowed.
+ */
+int fuse_file_cached_io_start(struct inode *inode, struct fuse_file *ff)
+{
+ struct fuse_inode *fi = get_fuse_inode(inode);
+ int err = 0;
+
+ /* There are no io modes if server does not implement open */
+ if (!ff->release_args)
+ return 0;
+
+ spin_lock(&fi->lock);
+ if (fi->iocachectr < 0) {
+ err = -ETXTBSY;
+ goto unlock;
+ }
+ WARN_ON(ff->iomode == IOM_UNCACHED);
+ if (ff->iomode == IOM_NONE) {
+ ff->iomode = IOM_CACHED;
+ if (fi->iocachectr == 0)
+ set_bit(FUSE_I_CACHE_IO_MODE, &fi->state);
+ fi->iocachectr++;
+ }
+unlock:
+ spin_unlock(&fi->lock);
+ return err;
+}
+
+static void fuse_file_cached_io_end(struct inode *inode, struct fuse_file *ff)
+{
+ struct fuse_inode *fi = get_fuse_inode(inode);
+
+ spin_lock(&fi->lock);
+ WARN_ON(fi->iocachectr <= 0);
+ WARN_ON(ff->iomode != IOM_CACHED);
+ ff->iomode = IOM_NONE;
+ fi->iocachectr--;
+ if (fi->iocachectr == 0)
+ clear_bit(FUSE_I_CACHE_IO_MODE, &fi->state);
+ spin_unlock(&fi->lock);
+}
+
+/* Start strictly uncached io mode where cache access is not allowed */
+static int fuse_file_uncached_io_start(struct inode *inode, struct fuse_file *ff)
+{
+ struct fuse_inode *fi = get_fuse_inode(inode);
+ int err = 0;
+
+ spin_lock(&fi->lock);
+ if (fi->iocachectr > 0) {
+ err = -ETXTBSY;
+ goto unlock;
+ }
+ WARN_ON(ff->iomode != IOM_NONE);
+ fi->iocachectr--;
+ ff->iomode = IOM_UNCACHED;
+unlock:
+ spin_unlock(&fi->lock);
+ return err;
+}
+
+static void fuse_file_uncached_io_end(struct inode *inode, struct fuse_file *ff)
+{
+ struct fuse_inode *fi = get_fuse_inode(inode);
+
+ spin_lock(&fi->lock);
+ WARN_ON(fi->iocachectr >= 0);
+ WARN_ON(ff->iomode != IOM_UNCACHED);
+ ff->iomode = IOM_NONE;
+ fi->iocachectr++;
+ spin_unlock(&fi->lock);
+}
+
+/* Request access to submit new io to inode via open file */
+int fuse_file_io_open(struct file *file, struct inode *inode)
+{
+ struct fuse_file *ff = file->private_data;
+ int err;
+
+ /*
+ * io modes are not relevant with DAX and with server that does not
+ * implement open.
+ */
+ if (FUSE_IS_DAX(inode) || !ff->release_args)
+ return 0;
+
+ /*
+ * FOPEN_PARALLEL_DIRECT_WRITES requires FOPEN_DIRECT_IO.
+ */
+ if (!(ff->open_flags & FOPEN_DIRECT_IO))
+ ff->open_flags &= ~FOPEN_PARALLEL_DIRECT_WRITES;
+
+ /*
+ * First parallel dio open denies caching inode io mode.
+ * First caching file open enters caching inode io mode.
+ *
+ * Note that if user opens a file open with O_DIRECT, but server did
+ * not specify FOPEN_DIRECT_IO, a later fcntl() could remove O_DIRECT,
+ * so we put the inode in caching mode to prevent parallel dio.
+ */
+ if (ff->open_flags & FOPEN_DIRECT_IO) {
+ if (ff->open_flags & FOPEN_PARALLEL_DIRECT_WRITES)
+ err = fuse_file_uncached_io_start(inode, ff);
+ else
+ return 0;
+ } else {
+ err = fuse_file_cached_io_start(inode, ff);
+ }
+ if (err)
+ goto fail;
+
+ return 0;
+
+fail:
+ pr_debug("failed to open file in requested io mode (open_flags=0x%x, err=%i).\n",
+ ff->open_flags, err);
+ /*
+ * The file open mode determines the inode io mode.
+ * Using incorrect open mode is a server mistake, which results in
+ * user visible failure of open() with EIO error.
+ */
+ return -EIO;
+}
+
+/* No more pending io and no new io possible to inode via open/mmapped file */
+void fuse_file_io_release(struct fuse_file *ff, struct inode *inode)
+{
+ /*
+ * Last parallel dio close allows caching inode io mode.
+ * Last caching file close exits caching inode io mode.
+ */
+ switch (ff->iomode) {
+ case IOM_NONE:
+ /* Nothing to do */
+ break;
+ case IOM_UNCACHED:
+ fuse_file_uncached_io_end(inode, ff);
+ break;
+ case IOM_CACHED:
+ fuse_file_cached_io_end(inode, ff);
+ break;
+ }
+}