1 files changed, 419 insertions, 0 deletions
diff --git a/fs/xfs/scrub/xfile.c b/fs/xfs/scrub/xfile.c
new file mode 100644
index 0000000000..090c3ead43
--- /dev/null
+++ b/fs/xfs/scrub/xfile.c
@@ -0,0 +1,419 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * Copyright (C) 2018-2023 Oracle.  All Rights Reserved.
+ * Author: Darrick J. Wong <djwong@kernel.org>
+ */
+#include "xfs.h"
+#include "xfs_fs.h"
+#include "xfs_shared.h"
+#include "xfs_format.h"
+#include "xfs_log_format.h"
+#include "xfs_trans_resv.h"
+#include "xfs_mount.h"
+#include "scrub/xfile.h"
+#include "scrub/xfarray.h"
+#include "scrub/scrub.h"
+#include "scrub/trace.h"
+#include <linux/shmem_fs.h>
+
+/*
+ * Swappable Temporary Memory
+ * ==========================
+ *
+ * Online checking sometimes needs to be able to stage a large amount of data
+ * in memory.  This information might not fit in the available memory and it
+ * doesn't all need to be accessible at all times.  In other words, we want an
+ * indexed data buffer to store data that can be paged out.
+ *
+ * When CONFIG_TMPFS=y, shmemfs is enough of a filesystem to meet those
+ * requirements.  Therefore, the xfile mechanism uses an unlinked shmem file to
+ * store our staging data.  This file is not installed in the file descriptor
+ * table so that user programs cannot access the data, which means that the
+ * xfile must be freed with xfile_destroy.
+ *
+ * xfiles assume that the caller will handle all required concurrency
+ * management; standard vfs locks (freezer and inode) are not taken.  Reads
+ * and writes are satisfied directly from the page cache.
+ *
+ * NOTE: The current shmemfs implementation has a quirk that in-kernel reads
+ * of a hole cause a page to be mapped into the file.  If you are going to
+ * create a sparse xfile, please be careful about reading from uninitialized
+ * parts of the file.  These pages are !Uptodate and will eventually be
+ * reclaimed if not written, but in the short term this boosts memory
+ * consumption.
+ */
+
+/*
+ * xfiles must not be exposed to userspace and require upper layers to
+ * coordinate access to the one handle returned by the constructor, so
+ * establish a separate lock class for xfiles to avoid confusing lockdep.
+ */
+static struct lock_class_key xfile_i_mutex_key;
+
+/*
+ * Create an xfile of the given size.  The description will be used in the
+ * trace output.
+ */
+int
+xfile_create(
+	const char		*description,
+	loff_t			isize,
+	struct xfile		**xfilep)
+{
+	struct inode		*inode;
+	struct xfile		*xf;
+	int			error = -ENOMEM;
+
+	xf = kmalloc(sizeof(struct xfile), XCHK_GFP_FLAGS);
+	if (!xf)
+		return -ENOMEM;
+
+	xf->file = shmem_file_setup(description, isize, 0);
+	if (!xf->file)
+		goto out_xfile;
+	if (IS_ERR(xf->file)) {
+		error = PTR_ERR(xf->file);
+		goto out_xfile;
+	}
+
+	/*
+	 * We want a large sparse file that we can pread, pwrite, and seek.
+	 * xfile users are responsible for keeping the xfile hidden away from
+	 * all other callers, so we skip timestamp updates and security checks.
+	 * Make the inode only accessible by root, just in case the xfile ever
+	 * escapes.
+	 */
+	xf->file->f_mode |= FMODE_PREAD | FMODE_PWRITE | FMODE_NOCMTIME |
+			    FMODE_LSEEK;
+	xf->file->f_flags |= O_RDWR | O_LARGEFILE | O_NOATIME;
+	inode = file_inode(xf->file);
+	inode->i_flags |= S_PRIVATE | S_NOCMTIME | S_NOATIME;
+	inode->i_mode &= ~0177;
+	inode->i_uid = GLOBAL_ROOT_UID;
+	inode->i_gid = GLOBAL_ROOT_GID;
+
+	lockdep_set_class(&inode->i_rwsem, &xfile_i_mutex_key);
+
+	trace_xfile_create(xf);
+
+	*xfilep = xf;
+	return 0;
+out_xfile:
+	kfree(xf);
+	return error;
+}
+
+/* Close the file and release all resources. */
+void
+xfile_destroy(
+	struct xfile		*xf)
+{
+	struct inode		*inode = file_inode(xf->file);
+
+	trace_xfile_destroy(xf);
+
+	lockdep_set_class(&inode->i_rwsem, &inode->i_sb->s_type->i_mutex_key);
+	fput(xf->file);
+	kfree(xf);
+}
+
+/*
+ * Read a memory object directly from the xfile's page cache.  Unlike regular
+ * pread, we return -E2BIG and -EFBIG for reads that are too large or at too
+ * high an offset, instead of truncating the read.  Otherwise, we return
+ * bytes read or an error code, like regular pread.
+ */
+ssize_t
+xfile_pread(
+	struct xfile		*xf,
+	void			*buf,
+	size_t			count,
+	loff_t			pos)
+{
+	struct inode		*inode = file_inode(xf->file);
+	struct address_space	*mapping = inode->i_mapping;
+	struct page		*page = NULL;
+	ssize_t			read = 0;
+	unsigned int		pflags;
+	int			error = 0;
+
+	if (count > MAX_RW_COUNT)
+		return -E2BIG;
+	if (inode->i_sb->s_maxbytes - pos < count)
+		return -EFBIG;
+
+	trace_xfile_pread(xf, pos, count);
+
+	pflags = memalloc_nofs_save();
+	while (count > 0) {
+		void		*p, *kaddr;
+		unsigned int	len;
+
+		len = min_t(ssize_t, count, PAGE_SIZE - offset_in_page(pos));
+
+		/*
+		 * In-kernel reads of a shmem file cause it to allocate a page
+		 * if the mapping shows a hole.  Therefore, if we hit ENOMEM
+		 * we can continue by zeroing the caller's buffer.
+		 */
+		page = shmem_read_mapping_page_gfp(mapping, pos >> PAGE_SHIFT,
+				__GFP_NOWARN);
+		if (IS_ERR(page)) {
+			error = PTR_ERR(page);
+			if (error != -ENOMEM)
+				break;
+
+			memset(buf, 0, len);
+			goto advance;
+		}
+
+		if (PageUptodate(page)) {
+			/*
+			 * xfile pages must never be mapped into userspace, so
+			 * we skip the dcache flush.
+			 */
+			kaddr = kmap_local_page(page);
+			p = kaddr + offset_in_page(pos);
+			memcpy(buf, p, len);
+			kunmap_local(kaddr);
+		} else {
+			memset(buf, 0, len);
+		}
+		put_page(page);
+
+advance:
+		count -= len;
+		pos += len;
+		buf += len;
+		read += len;
+	}
+	memalloc_nofs_restore(pflags);
+
+	if (read > 0)
+		return read;
+	return error;
+}
+
+/*
+ * Write a memory object directly to the xfile's page cache.  Unlike regular
+ * pwrite, we return -E2BIG and -EFBIG for writes that are too large or at too
+ * high an offset, instead of truncating the write.  Otherwise, we return
+ * bytes written or an error code, like regular pwrite.
+ */
+ssize_t
+xfile_pwrite(
+	struct xfile		*xf,
+	const void		*buf,
+	size_t			count,
+	loff_t			pos)
+{
+	struct inode		*inode = file_inode(xf->file);
+	struct address_space	*mapping = inode->i_mapping;
+	const struct address_space_operations *aops = mapping->a_ops;
+	struct page		*page = NULL;
+	ssize_t			written = 0;
+	unsigned int		pflags;
+	int			error = 0;
+
+	if (count > MAX_RW_COUNT)
+		return -E2BIG;
+	if (inode->i_sb->s_maxbytes - pos < count)
+		return -EFBIG;
+
+	trace_xfile_pwrite(xf, pos, count);
+
+	pflags = memalloc_nofs_save();
+	while (count > 0) {
+		void		*fsdata = NULL;
+		void		*p, *kaddr;
+		unsigned int	len;
+		int		ret;
+
+		len = min_t(ssize_t, count, PAGE_SIZE - offset_in_page(pos));
+
+		/*
+		 * We call write_begin directly here to avoid all the freezer
+		 * protection lock-taking that happens in the normal path.
+		 * shmem doesn't support fs freeze, but lockdep doesn't know
+		 * that and will trip over that.
+		 */
+		error = aops->write_begin(NULL, mapping, pos, len, &page,
+				&fsdata);
+		if (error)
+			break;
+
+		/*
+		 * xfile pages must never be mapped into userspace, so we skip
+		 * the dcache flush.  If the page is not uptodate, zero it
+		 * before writing data.
+		 */
+		kaddr = kmap_local_page(page);
+		if (!PageUptodate(page)) {
+			memset(kaddr, 0, PAGE_SIZE);
+			SetPageUptodate(page);
+		}
+		p = kaddr + offset_in_page(pos);
+		memcpy(p, buf, len);
+		kunmap_local(kaddr);
+
+		ret = aops->write_end(NULL, mapping, pos, len, len, page,
+				fsdata);
+		if (ret < 0) {
+			error = ret;
+			break;
+		}
+
+		written += ret;
+		if (ret != len)
+			break;
+
+		count -= ret;
+		pos += ret;
+		buf += ret;
+	}
+	memalloc_nofs_restore(pflags);
+
+	if (written > 0)
+		return written;
+	return error;
+}
+
+/* Find the next written area in the xfile data for a given offset. */
+loff_t
+xfile_seek_data(
+	struct xfile		*xf,
+	loff_t			pos)
+{
+	loff_t			ret;
+
+	ret = vfs_llseek(xf->file, pos, SEEK_DATA);
+	trace_xfile_seek_data(xf, pos, ret);
+	return ret;
+}
+
+/* Query stat information for an xfile. */
+int
+xfile_stat(
+	struct xfile		*xf,
+	struct xfile_stat	*statbuf)
+{
+	struct kstat		ks;
+	int			error;
+
+	error = vfs_getattr_nosec(&xf->file->f_path, &ks,
+			STATX_SIZE | STATX_BLOCKS, AT_STATX_DONT_SYNC);
+	if (error)
+		return error;
+
+	statbuf->size = ks.size;
+	statbuf->bytes = ks.blocks << SECTOR_SHIFT;
+	return 0;
+}
+
+/*
+ * Grab the (locked) page for a memory object.  The object cannot span a page
+ * boundary.  Returns 0 (and a locked page) if successful, -ENOTBLK if we
+ * cannot grab the page, or the usual negative errno.
+ */
+int
+xfile_get_page(
+	struct xfile		*xf,
+	loff_t			pos,
+	unsigned int		len,
+	struct xfile_page	*xfpage)
+{
+	struct inode		*inode = file_inode(xf->file);
+	struct address_space	*mapping = inode->i_mapping;
+	const struct address_space_operations *aops = mapping->a_ops;
+	struct page		*page = NULL;
+	void			*fsdata = NULL;
+	loff_t			key = round_down(pos, PAGE_SIZE);
+	unsigned int		pflags;
+	int			error;
+
+	if (inode->i_sb->s_maxbytes - pos < len)
+		return -ENOMEM;
+	if (len > PAGE_SIZE - offset_in_page(pos))
+		return -ENOTBLK;
+
+	trace_xfile_get_page(xf, pos, len);
+
+	pflags = memalloc_nofs_save();
+
+	/*
+	 * We call write_begin directly here to avoid all the freezer
+	 * protection lock-taking that happens in the normal path.  shmem
+	 * doesn't support fs freeze, but lockdep doesn't know that and will
+	 * trip over that.
+	 */
+	error = aops->write_begin(NULL, mapping, key, PAGE_SIZE, &page,
+			&fsdata);
+	if (error)
+		goto out_pflags;
+
+	/* We got the page, so make sure we push out EOF. */
+	if (i_size_read(inode) < pos + len)
+		i_size_write(inode, pos + len);
+
+	/*
+	 * If the page isn't up to date, fill it with zeroes before we hand it
+	 * to the caller and make sure the backing store will hold on to them.
+	 */
+	if (!PageUptodate(page)) {
+		void	*kaddr;
+
+		kaddr = kmap_local_page(page);
+		memset(kaddr, 0, PAGE_SIZE);
+		kunmap_local(kaddr);
+		SetPageUptodate(page);
+	}
+
+	/*
+	 * Mark each page dirty so that the contents are written to some
+	 * backing store when we drop this buffer, and take an extra reference
+	 * to prevent the xfile page from being swapped or removed from the
+	 * page cache by reclaim if the caller unlocks the page.
+	 */
+	set_page_dirty(page);
+	get_page(page);
+
+	xfpage->page = page;
+	xfpage->fsdata = fsdata;
+	xfpage->pos = key;
+out_pflags:
+	memalloc_nofs_restore(pflags);
+	return error;
+}
+
+/*
+ * Release the (locked) page for a memory object.  Returns 0 or a negative
+ * errno.
+ */
+int
+xfile_put_page(
+	struct xfile		*xf,
+	struct xfile_page	*xfpage)
+{
+	struct inode		*inode = file_inode(xf->file);
+	struct address_space	*mapping = inode->i_mapping;
+	const struct address_space_operations *aops = mapping->a_ops;
+	unsigned int		pflags;
+	int			ret;
+
+	trace_xfile_put_page(xf, xfpage->pos, PAGE_SIZE);
+
+	/* Give back the reference that we took in xfile_get_page. */
+	put_page(xfpage->page);
+
+	pflags = memalloc_nofs_save();
+	ret = aops->write_end(NULL, mapping, xfpage->pos, PAGE_SIZE, PAGE_SIZE,
+			xfpage->page, xfpage->fsdata);
+	memalloc_nofs_restore(pflags);
+	memset(xfpage, 0, sizeof(struct xfile_page));
+
+	if (ret < 0)
+		return ret;
+	if (ret != PAGE_SIZE)
+		return -EIO;
+	return 0;
+}