1 files changed, 273 insertions, 0 deletions
diff --git a/fs/ramfs/file-nommu.c b/fs/ramfs/file-nommu.c
new file mode 100644
index 000000000..cb240eac5
--- /dev/null
+++ b/fs/ramfs/file-nommu.c
@@ -0,0 +1,273 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/* file-nommu.c: no-MMU version of ramfs
+ *
+ * Copyright (C) 2005 Red Hat, Inc. All Rights Reserved.
+ * Written by David Howells (dhowells@redhat.com)
+ */
+
+#include <linux/module.h>
+#include <linux/fs.h>
+#include <linux/mm.h>
+#include <linux/pagemap.h>
+#include <linux/highmem.h>
+#include <linux/init.h>
+#include <linux/string.h>
+#include <linux/backing-dev.h>
+#include <linux/ramfs.h>
+#include <linux/pagevec.h>
+#include <linux/mman.h>
+#include <linux/sched.h>
+#include <linux/slab.h>
+
+#include <linux/uaccess.h>
+#include "internal.h"
+
+static int ramfs_nommu_setattr(struct user_namespace *, struct dentry *, struct iattr *);
+static unsigned long ramfs_nommu_get_unmapped_area(struct file *file,
+						   unsigned long addr,
+						   unsigned long len,
+						   unsigned long pgoff,
+						   unsigned long flags);
+static int ramfs_nommu_mmap(struct file *file, struct vm_area_struct *vma);
+
+static unsigned ramfs_mmap_capabilities(struct file *file)
+{
+	return NOMMU_MAP_DIRECT | NOMMU_MAP_COPY | NOMMU_MAP_READ |
+		NOMMU_MAP_WRITE | NOMMU_MAP_EXEC;
+}
+
+const struct file_operations ramfs_file_operations = {
+	.mmap_capabilities	= ramfs_mmap_capabilities,
+	.mmap			= ramfs_nommu_mmap,
+	.get_unmapped_area	= ramfs_nommu_get_unmapped_area,
+	.read_iter		= generic_file_read_iter,
+	.write_iter		= generic_file_write_iter,
+	.fsync			= noop_fsync,
+	.splice_read		= generic_file_splice_read,
+	.splice_write		= iter_file_splice_write,
+	.llseek			= generic_file_llseek,
+};
+
+const struct inode_operations ramfs_file_inode_operations = {
+	.setattr		= ramfs_nommu_setattr,
+	.getattr		= simple_getattr,
+};
+
+/*****************************************************************************/
+/*
+ * add a contiguous set of pages into a ramfs inode when it's truncated from
+ * size 0 on the assumption that it's going to be used for an mmap of shared
+ * memory
+ */
+int ramfs_nommu_expand_for_mapping(struct inode *inode, size_t newsize)
+{
+	unsigned long npages, xpages, loop;
+	struct page *pages;
+	unsigned order;
+	void *data;
+	int ret;
+	gfp_t gfp = mapping_gfp_mask(inode->i_mapping);
+
+	/* make various checks */
+	order = get_order(newsize);
+	if (unlikely(order >= MAX_ORDER))
+		return -EFBIG;
+
+	ret = inode_newsize_ok(inode, newsize);
+	if (ret)
+		return ret;
+
+	i_size_write(inode, newsize);
+
+	/* allocate enough contiguous pages to be able to satisfy the
+	 * request */
+	pages = alloc_pages(gfp, order);
+	if (!pages)
+		return -ENOMEM;
+
+	/* split the high-order page into an array of single pages */
+	xpages = 1UL << order;
+	npages = (newsize + PAGE_SIZE - 1) >> PAGE_SHIFT;
+
+	split_page(pages, order);
+
+	/* trim off any pages we don't actually require */
+	for (loop = npages; loop < xpages; loop++)
+		__free_page(pages + loop);
+
+	/* clear the memory we allocated */
+	newsize = PAGE_SIZE * npages;
+	data = page_address(pages);
+	memset(data, 0, newsize);
+
+	/* attach all the pages to the inode's address space */
+	for (loop = 0; loop < npages; loop++) {
+		struct page *page = pages + loop;
+
+		ret = add_to_page_cache_lru(page, inode->i_mapping, loop,
+					gfp);
+		if (ret < 0)
+			goto add_error;
+
+		/* prevent the page from being discarded on memory pressure */
+		SetPageDirty(page);
+		SetPageUptodate(page);
+
+		unlock_page(page);
+		put_page(page);
+	}
+
+	return 0;
+
+add_error:
+	while (loop < npages)
+		__free_page(pages + loop++);
+	return ret;
+}
+
+/*****************************************************************************/
+/*
+ *
+ */
+static int ramfs_nommu_resize(struct inode *inode, loff_t newsize, loff_t size)
+{
+	int ret;
+
+	/* assume a truncate from zero size is going to be for the purposes of
+	 * shared mmap */
+	if (size == 0) {
+		if (unlikely(newsize >> 32))
+			return -EFBIG;
+
+		return ramfs_nommu_expand_for_mapping(inode, newsize);
+	}
+
+	/* check that a decrease in size doesn't cut off any shared mappings */
+	if (newsize < size) {
+		ret = nommu_shrink_inode_mappings(inode, size, newsize);
+		if (ret < 0)
+			return ret;
+	}
+
+	truncate_setsize(inode, newsize);
+	return 0;
+}
+
+/*****************************************************************************/
+/*
+ * handle a change of attributes
+ * - we're specifically interested in a change of size
+ */
+static int ramfs_nommu_setattr(struct user_namespace *mnt_userns,
+			       struct dentry *dentry, struct iattr *ia)
+{
+	struct inode *inode = d_inode(dentry);
+	unsigned int old_ia_valid = ia->ia_valid;
+	int ret = 0;
+
+	/* POSIX UID/GID verification for setting inode attributes */
+	ret = setattr_prepare(&init_user_ns, dentry, ia);
+	if (ret)
+		return ret;
+
+	/* pick out size-changing events */
+	if (ia->ia_valid & ATTR_SIZE) {
+		loff_t size = inode->i_size;
+
+		if (ia->ia_size != size) {
+			ret = ramfs_nommu_resize(inode, ia->ia_size, size);
+			if (ret < 0 || ia->ia_valid == ATTR_SIZE)
+				goto out;
+		} else {
+			/* we skipped the truncate but must still update
+			 * timestamps
+			 */
+			ia->ia_valid |= ATTR_MTIME|ATTR_CTIME;
+		}
+	}
+
+	setattr_copy(&init_user_ns, inode, ia);
+ out:
+	ia->ia_valid = old_ia_valid;
+	return ret;
+}
+
+/*****************************************************************************/
+/*
+ * try to determine where a shared mapping can be made
+ * - we require that:
+ *   - the pages to be mapped must exist
+ *   - the pages be physically contiguous in sequence
+ */
+static unsigned long ramfs_nommu_get_unmapped_area(struct file *file,
+					    unsigned long addr, unsigned long len,
+					    unsigned long pgoff, unsigned long flags)
+{
+	unsigned long maxpages, lpages, nr_folios, loop, ret, nr_pages, pfn;
+	struct inode *inode = file_inode(file);
+	struct folio_batch fbatch;
+	loff_t isize;
+
+	/* the mapping mustn't extend beyond the EOF */
+	lpages = (len + PAGE_SIZE - 1) >> PAGE_SHIFT;
+	isize = i_size_read(inode);
+
+	ret = -ENOSYS;
+	maxpages = (isize + PAGE_SIZE - 1) >> PAGE_SHIFT;
+	if (pgoff >= maxpages)
+		goto out;
+
+	if (maxpages - pgoff < lpages)
+		goto out;
+
+	/* gang-find the pages */
+	folio_batch_init(&fbatch);
+	nr_pages = 0;
+repeat:
+	nr_folios = filemap_get_folios_contig(inode->i_mapping, &pgoff,
+			ULONG_MAX, &fbatch);
+	if (!nr_folios) {
+		ret = -ENOSYS;
+		return ret;
+	}
+
+	if (ret == -ENOSYS) {
+		ret = (unsigned long) folio_address(fbatch.folios[0]);
+		pfn = folio_pfn(fbatch.folios[0]);
+	}
+	/* check the pages for physical adjacency */
+	for (loop = 0; loop < nr_folios; loop++) {
+		if (pfn + nr_pages != folio_pfn(fbatch.folios[loop])) {
+			ret = -ENOSYS;
+			goto out_free; /* leave if not physical adjacent */
+		}
+		nr_pages += folio_nr_pages(fbatch.folios[loop]);
+		if (nr_pages >= lpages)
+			goto out_free; /* successfully found desired pages*/
+	}
+
+	if (nr_pages < lpages) {
+		folio_batch_release(&fbatch);
+		goto repeat; /* loop if pages are missing */
+	}
+	/* okay - all conditions fulfilled */
+
+out_free:
+	folio_batch_release(&fbatch);
+out:
+	return ret;
+}
+
+/*****************************************************************************/
+/*
+ * set up a mapping for shared memory segments
+ */
+static int ramfs_nommu_mmap(struct file *file, struct vm_area_struct *vma)
+{
+	if (!(vma->vm_flags & (VM_SHARED | VM_MAYSHARE)))
+		return -ENOSYS;
+
+	file_accessed(file);
+	vma->vm_ops = &generic_file_vm_ops;
+	return 0;
+}