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From: John Groves <John@Groves.net>
To: John Groves <jgroves@micron.com>,
	Jonathan Corbet <corbet@lwn.net>,
	Dan Williams <dan.j.williams@intel.com>,
	Vishal Verma <vishal.l.verma@intel.com>,
	Dave Jiang <dave.jiang@intel.com>,
	Alexander Viro <viro@zeniv.linux.org.uk>,
	Christian Brauner <brauner@kernel.org>, Jan Kara <jack@suse.cz>,
	Matthew Wilcox <willy@infradead.org>,
	linux-cxl@vger.kernel.org, linux-fsdevel@vger.kernel.org,
	linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org,
	nvdimm@lists.linux.dev
Cc: John@Groves.net, john@jagalactic.com,
	Dave Chinner <david@fromorbit.com>,
	Christoph Hellwig <hch@infradead.org>,
	dave.hansen@linux.intel.com, gregory.price@memverge.com,
	John Groves <john@groves.net>
Subject: [RFC PATCH 13/20] famfs: Add iomap_ops
Date: Fri, 23 Feb 2024 11:41:57 -0600	[thread overview]
Message-ID: <2996a7e757c3762a9a28c789645acd289f5f7bc0.1708709155.git.john@groves.net> (raw)
In-Reply-To: <cover.1708709155.git.john@groves.net>

This commit introduces the famfs iomap_ops. When either
dax_iomap_fault() or dax_iomap_rw() is called, we get a callback
via our iomap_begin() handler. The question being asked is
"please resolve (file, offset) to (daxdev, offset)". The function
famfs_meta_to_dax_offset() does this.

The per-file metadata is just an extent list to the
backing dax dev.  The order of this resolution is O(N) for N
extents. Note with the current user space, files usually have
only one extent.

Signed-off-by: John Groves <john@groves.net>
---
 fs/famfs/famfs_file.c | 245 ++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 245 insertions(+)
 create mode 100644 fs/famfs/famfs_file.c

diff --git a/fs/famfs/famfs_file.c b/fs/famfs/famfs_file.c
new file mode 100644
index 000000000000..fc667d5f7be8
--- /dev/null
+++ b/fs/famfs/famfs_file.c
@@ -0,0 +1,245 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * famfs - dax file system for shared fabric-attached memory
+ *
+ * Copyright 2023-2024 Micron Technology, Inc.
+ *
+ * This file system, originally based on ramfs the dax support from xfs,
+ * is intended to allow multiple host systems to mount a common file system
+ * view of dax files that map to shared memory.
+ */
+
+#include <linux/module.h>
+#include <linux/fs.h>
+#include <linux/mm.h>
+#include <linux/sched.h>
+#include <linux/dax.h>
+#include <linux/uio.h>
+#include <linux/iomap.h>
+#include <uapi/linux/famfs_ioctl.h>
+#include "famfs_internal.h"
+
+/*********************************************************************
+ * iomap_operations
+ *
+ * This stuff uses the iomap (dax-related) helpers to resolve file offsets to
+ * offsets within a dax device.
+ */
+
+/**
+ * famfs_meta_to_dax_offset()
+ *
+ * This function is called by famfs_iomap_begin() to resolve an offset in a file to
+ * an offset in a dax device. This is upcalled from dax from calls to both
+ * dax_iomap_fault() and dax_iomap_rw(). Dax finishes the job resolving a fault to
+ * a specific physical page (the fault case) or doing a memcpy variant (the rw case)
+ *
+ * Pages can be PTE (4k), PMD (2MiB) or (theoretically) PuD (1GiB)
+ * (these sizes are for X86; may vary on other cpu architectures
+ *
+ * @inode  - the file where the fault occurred
+ * @iomap  - struct iomap to be filled in to indicate where to find the right memory, relative
+ *           to a dax device.
+ * @offset - the offset within the file where the fault occurred (will be page boundary)
+ * @len    - the length of the faulted mapping (will be a page multiple)
+ *           (will be trimmed in *iomap if it's disjoint in the extent list)
+ * @flags
+ */
+static int
+famfs_meta_to_dax_offset(
+	struct inode *inode,
+	struct iomap *iomap,
+	loff_t        offset,
+	loff_t        len,
+	unsigned int  flags)
+{
+	struct famfs_file_meta *meta = (struct famfs_file_meta *)inode->i_private;
+	int i;
+	loff_t local_offset = offset;
+	struct famfs_fs_info  *fsi = inode->i_sb->s_fs_info;
+
+	iomap->offset = offset; /* file offset */
+
+	for (i = 0; i < meta->tfs_extent_ct; i++) {
+		loff_t dax_ext_offset = meta->tfs_extents[i].offset;
+		loff_t dax_ext_len    = meta->tfs_extents[i].len;
+
+		if ((dax_ext_offset == 0) && (meta->file_type != FAMFS_SUPERBLOCK))
+			pr_err("%s: zero offset on non-superblock file!!\n", __func__);
+
+		/* local_offset is the offset minus the size of extents skipped so far;
+		 * If local_offset < dax_ext_len, the data of interest starts in this extent
+		 */
+		if (local_offset < dax_ext_len) {
+			loff_t ext_len_remainder = dax_ext_len - local_offset;
+
+			/*+
+			 * OK, we found the file metadata extent where this data begins
+			 * @local_offset      - The offset within the current extent
+			 * @ext_len_remainder - Remaining length of ext after skipping local_offset
+			 *
+			 * iomap->addr is the offset within the dax device where that data
+			 * starts
+			 */
+			iomap->addr    = dax_ext_offset + local_offset; /* dax dev offset */
+			iomap->offset  = offset; /* file offset */
+			iomap->length  = min_t(loff_t, len, ext_len_remainder);
+			iomap->dax_dev = fsi->dax_devp;
+			iomap->type    = IOMAP_MAPPED;
+			iomap->flags   = flags;
+
+			return 0;
+		}
+		local_offset -= dax_ext_len; /* Get ready for the next extent */
+	}
+
+	/* Set iomap to zero length in this case, and return 0
+	 * This just means that the r/w is past EOF
+	 */
+	iomap->addr    = offset;
+	iomap->offset  = offset; /* file offset */
+	iomap->length  = 0; /* this had better result in no access to dax mem */
+	iomap->dax_dev = fsi->dax_devp;
+	iomap->type    = IOMAP_MAPPED;
+	iomap->flags   = flags;
+
+	return 0;
+}
+
+/**
+ * famfs_iomap_begin()
+ *
+ * This function is pretty simple because files are
+ * * never partially allocated
+ * * never have holes (never sparse)
+ * * never "allocate on write"
+ */
+static int
+famfs_iomap_begin(
+	struct inode	       *inode,
+	loff_t			offset,
+	loff_t			length,
+	unsigned int		flags,
+	struct iomap	       *iomap,
+	struct iomap	       *srcmap)
+{
+	struct famfs_file_meta *meta = inode->i_private;
+	size_t size;
+	int rc;
+
+	size = i_size_read(inode);
+
+	WARN_ON(size != meta->file_size);
+
+	rc = famfs_meta_to_dax_offset(inode, iomap, offset, length, flags);
+
+	return rc;
+}
+
+/* Note: We never need a special set of write_iomap_ops because famfs never
+ * performs allocation on write.
+ */
+const struct iomap_ops famfs_iomap_ops = {
+	.iomap_begin		= famfs_iomap_begin,
+};
+
+/*********************************************************************
+ * vm_operations
+ */
+static vm_fault_t
+__famfs_filemap_fault(
+	struct vm_fault		*vmf,
+	unsigned int		pe_size,
+	bool			write_fault)
+{
+	struct inode		*inode = file_inode(vmf->vma->vm_file);
+	vm_fault_t		ret;
+
+	if (write_fault) {
+		sb_start_pagefault(inode->i_sb);
+		file_update_time(vmf->vma->vm_file);
+	}
+
+	if (IS_DAX(inode)) {
+		pfn_t pfn;
+
+		ret = dax_iomap_fault(vmf, pe_size, &pfn, NULL, &famfs_iomap_ops);
+		if (ret & VM_FAULT_NEEDDSYNC)
+			ret = dax_finish_sync_fault(vmf, pe_size, pfn);
+	} else {
+		/* All famfs faults will be dax... */
+		pr_err("%s: oops, non-dax fault\n", __func__);
+		ret = VM_FAULT_SIGBUS;
+	}
+
+	if (write_fault)
+		sb_end_pagefault(inode->i_sb);
+
+	return ret;
+}
+
+static inline bool
+famfs_is_write_fault(
+	struct vm_fault		*vmf)
+{
+	return (vmf->flags & FAULT_FLAG_WRITE) &&
+	       (vmf->vma->vm_flags & VM_SHARED);
+}
+
+static vm_fault_t
+famfs_filemap_fault(
+	struct vm_fault		*vmf)
+{
+	/* DAX can shortcut the normal fault path on write faults! */
+	return __famfs_filemap_fault(vmf, 0,
+			IS_DAX(file_inode(vmf->vma->vm_file)) && famfs_is_write_fault(vmf));
+}
+
+static vm_fault_t
+famfs_filemap_huge_fault(
+	struct vm_fault	*vmf,
+	unsigned int	 pe_size)
+{
+	if (!IS_DAX(file_inode(vmf->vma->vm_file))) {
+		pr_err("%s: file not marked IS_DAX!!\n", __func__);
+		return VM_FAULT_SIGBUS;
+	}
+
+	/* DAX can shortcut the normal fault path on write faults! */
+	return __famfs_filemap_fault(vmf, pe_size, famfs_is_write_fault(vmf));
+}
+
+static vm_fault_t
+famfs_filemap_page_mkwrite(
+	struct vm_fault		*vmf)
+{
+	return __famfs_filemap_fault(vmf, 0, true);
+}
+
+static vm_fault_t
+famfs_filemap_pfn_mkwrite(
+	struct vm_fault		*vmf)
+{
+	return __famfs_filemap_fault(vmf, 0, true);
+}
+
+static vm_fault_t
+famfs_filemap_map_pages(
+	struct vm_fault	       *vmf,
+	pgoff_t			start_pgoff,
+	pgoff_t			end_pgoff)
+{
+	vm_fault_t ret;
+
+	ret = filemap_map_pages(vmf, start_pgoff, end_pgoff);
+	return ret;
+}
+
+const struct vm_operations_struct famfs_file_vm_ops = {
+	.fault		= famfs_filemap_fault,
+	.huge_fault	= famfs_filemap_huge_fault,
+	.map_pages	= famfs_filemap_map_pages,
+	.page_mkwrite	= famfs_filemap_page_mkwrite,
+	.pfn_mkwrite	= famfs_filemap_pfn_mkwrite,
+};
+
-- 
2.43.0


  parent reply	other threads:[~2024-02-23 17:42 UTC|newest]

Thread overview: 95+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2024-02-23 17:41 [RFC PATCH 00/20] Introduce the famfs shared-memory file system John Groves
2024-02-23 17:41 ` [RFC PATCH 01/20] famfs: Documentation John Groves
2024-02-23 17:41 ` [RFC PATCH 02/20] dev_dax_iomap: Add fs_dax_get() func to prepare dax for fs-dax usage John Groves
2024-02-26 12:05   ` Jonathan Cameron
2024-02-26 15:00     ` John Groves
2024-02-23 17:41 ` [RFC PATCH 03/20] dev_dax_iomap: Move dax_pgoff_to_phys from device.c to bus.c since both need it now John Groves
2024-02-26 12:10   ` Jonathan Cameron
2024-02-26 15:13     ` John Groves
2024-02-23 17:41 ` [RFC PATCH 04/20] dev_dax_iomap: Save the kva from memremap John Groves
2024-02-26 12:21   ` Jonathan Cameron
2024-02-26 15:48     ` John Groves
2024-02-23 17:41 ` [RFC PATCH 05/20] dev_dax_iomap: Add dax_operations for use by fs-dax on devdax John Groves
2024-02-26 12:32   ` Jonathan Cameron
2024-02-26 16:09     ` John Groves
2024-02-23 17:41 ` [RFC PATCH 06/20] dev_dax_iomap: Add CONFIG_DEV_DAX_IOMAP kernel build parameter John Groves
2024-02-26 12:34   ` Jonathan Cameron
2024-02-26 16:12     ` John Groves
2024-02-23 17:41 ` [RFC PATCH 07/20] famfs: Add include/linux/famfs_ioctl.h John Groves
2024-02-24  1:39   ` Randy Dunlap
2024-02-24  2:23     ` John Groves
2024-02-24  3:27       ` Randy Dunlap
2024-02-24 23:32         ` John Groves
2024-02-24 23:40           ` Randy Dunlap
2024-02-26 12:39   ` Jonathan Cameron
2024-02-26 16:44     ` John Groves
2024-02-26 16:56       ` Jonathan Cameron
2024-02-26 18:04         ` John Groves
2024-02-23 17:41 ` [RFC PATCH 08/20] famfs: Add famfs_internal.h John Groves
2024-02-26 12:48   ` Jonathan Cameron
2024-02-26 17:35     ` John Groves
2024-02-27 10:28       ` Jonathan Cameron
2024-02-28  1:06         ` John Groves
2024-02-27 13:38   ` Christian Brauner
2024-02-27 14:12     ` John Groves
2024-02-23 17:41 ` [RFC PATCH 09/20] famfs: Add super_operations John Groves
2024-02-26 12:51   ` Jonathan Cameron
2024-02-26 21:47     ` John Groves
2024-02-27 10:34       ` Jonathan Cameron
2024-02-27 17:48     ` John Groves
2024-02-23 17:41 ` [RFC PATCH 10/20] famfs: famfs_open_device() & dax_holder_operations John Groves
2024-02-26 12:56   ` Jonathan Cameron
2024-02-26 22:22     ` John Groves
2024-02-27 13:39   ` Christian Brauner
2024-02-27 18:38     ` John Groves
2024-02-23 17:41 ` [RFC PATCH 11/20] famfs: Add fs_context_operations John Groves
2024-02-26 13:20   ` Jonathan Cameron
2024-02-26 22:43     ` John Groves
2024-02-27 13:41   ` Christian Brauner
2024-02-28  0:59     ` John Groves
2024-02-28  1:49       ` Randy Dunlap
2024-02-28  8:17         ` Christian Brauner
2024-02-28 10:07       ` Christian Brauner
2024-02-28 12:01         ` Christian Brauner
2024-02-23 17:41 ` [RFC PATCH 12/20] famfs: Add inode_operations and file_system_type John Groves
2024-02-26 13:25   ` Jonathan Cameron
2024-02-26 22:53     ` John Groves
2024-02-23 17:41 ` John Groves [this message]
2024-02-26 13:30   ` [RFC PATCH 13/20] famfs: Add iomap_ops Jonathan Cameron
2024-02-26 23:00     ` John Groves
2024-02-23 17:41 ` [RFC PATCH 14/20] famfs: Add struct file_operations John Groves
2024-02-26 13:32   ` Jonathan Cameron
2024-02-26 23:09     ` John Groves
2024-02-23 17:41 ` [RFC PATCH 15/20] famfs: Add ioctl to file_operations John Groves
2024-02-26 13:44   ` Jonathan Cameron
2024-02-23 17:42 ` [RFC PATCH 16/20] famfs: Add fault counters John Groves
2024-02-23 18:23   ` Dave Hansen
2024-02-23 19:56     ` John Groves
2024-02-23 20:04       ` Dan Williams
2024-02-23 20:39         ` John Groves
2024-02-23 21:19           ` Dave Hansen
2024-02-23 23:50             ` Dan Williams
2024-02-24  3:59               ` Matthew Wilcox
2024-02-24  4:30                 ` Dan Williams
2024-02-23 17:42 ` [RFC PATCH 17/20] famfs: Add module stuff John Groves
2024-02-26 13:47   ` Jonathan Cameron
2024-02-27 22:15     ` John Groves
2024-02-23 17:42 ` [RFC PATCH 18/20] famfs: Support character dax via the dev_dax_iomap patch John Groves
2024-02-26 13:52   ` Jonathan Cameron
2024-02-27 22:27     ` John Groves
2024-02-23 17:42 ` [RFC PATCH 19/20] famfs: Update MAINTAINERS file John Groves
2024-02-23 17:42 ` [RFC PATCH 20/20] famfs: Add Kconfig and Makefile plumbing John Groves
2024-02-24  1:50   ` Randy Dunlap
2024-02-24  2:24     ` John Groves
2024-02-24  0:07 ` [RFC PATCH 00/20] Introduce the famfs shared-memory file system Luis Chamberlain
2024-02-26 13:27   ` John Groves
2024-02-26 15:53     ` Luis Chamberlain
2024-02-26 21:16       ` John Groves
2024-02-27  0:58         ` Luis Chamberlain
2024-02-27  2:05           ` John Groves
2024-02-29  2:15             ` Dave Chinner
2024-02-29 14:52               ` John Groves
2024-03-11  1:29                 ` Dave Chinner
2024-02-29  6:52 ` Amir Goldstein
2024-02-29 22:16   ` John Groves
2024-05-17  9:55   ` Miklos Szeredi

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