Date:   Tue, 10 Sep 2019 21:21:10 +0530
From:   Chandan Rajendra <chandan@...ux.ibm.com>
To:     viro@...iv.linux.org.uk, linux-fsdevel@...r.kernel.org,
        linux-ext4@...r.kernel.org, linux-fscrypt@...r.kernel.org
Cc:     Chandan Rajendra <chandan@...ux.ibm.com>, tytso@....edu,
        adilger.kernel@...ger.ca, ebiggers@...nel.org, hch@...radead.org,
        chandanrlinux@...il.com
Subject: [PATCH RESEND V5 2/7] FS: Introduce read callbacks

Read callbacks implements a state machine to be executed after a
buffered read I/O is completed. They help in further processing the file
data read from the backing store. Currently, decryption is the only post
processing step to be supported.

The execution of the state machine is to be initiated by the endio
function associated with the read operation.

Signed-off-by: Chandan Rajendra <chandan@...ux.ibm.com>
---
 fs/Kconfig                     |   3 +
 fs/Makefile                    |   1 +
 fs/ext4/Kconfig                |   1 +
 fs/f2fs/Kconfig                |   1 +
 fs/read_callbacks.c            | 285 +++++++++++++++++++++++++++++++++
 include/linux/read_callbacks.h |  48 ++++++
 6 files changed, 339 insertions(+)
 create mode 100644 fs/read_callbacks.c
 create mode 100644 include/linux/read_callbacks.h

diff --git a/fs/Kconfig b/fs/Kconfig
index 3e6d3101f3ff..2d96a58d7418 100644
--- a/fs/Kconfig
+++ b/fs/Kconfig
@@ -20,6 +20,9 @@ if BLOCK
 config FS_IOMAP
 	bool
 
+config FS_READ_CALLBACKS
+	bool
+
 source "fs/ext2/Kconfig"
 source "fs/ext4/Kconfig"
 source "fs/jbd2/Kconfig"
diff --git a/fs/Makefile b/fs/Makefile
index 427fec226fae..942808f83472 100644
--- a/fs/Makefile
+++ b/fs/Makefile
@@ -53,6 +53,7 @@ obj-$(CONFIG_SYSCTL)		+= drop_caches.o
 
 obj-$(CONFIG_FHANDLE)		+= fhandle.o
 obj-$(CONFIG_FS_IOMAP)		+= iomap.o
+obj-$(CONFIG_FS_READ_CALLBACKS) += read_callbacks.o
 
 obj-y				+= quota/
 
diff --git a/fs/ext4/Kconfig b/fs/ext4/Kconfig
index 06f77ca7f36e..2e24df67f085 100644
--- a/fs/ext4/Kconfig
+++ b/fs/ext4/Kconfig
@@ -38,6 +38,7 @@ config EXT4_FS
 	select CRYPTO
 	select CRYPTO_CRC32C
 	select FS_IOMAP
+	select FS_READ_CALLBACKS if FS_ENCRYPTION
 	help
 	  This is the next generation of the ext3 filesystem.
 
diff --git a/fs/f2fs/Kconfig b/fs/f2fs/Kconfig
index e57cc754d543..1e1424940d1b 100644
--- a/fs/f2fs/Kconfig
+++ b/fs/f2fs/Kconfig
@@ -4,6 +4,7 @@ config F2FS_FS
 	select CRYPTO
 	select CRYPTO_CRC32
 	select F2FS_FS_XATTR if FS_ENCRYPTION
+	select FS_READ_CALLBACKS if FS_ENCRYPTION
 	help
 	  F2FS is based on Log-structured File System (LFS), which supports
 	  versatile "flash-friendly" features. The design has been focused on
diff --git a/fs/read_callbacks.c b/fs/read_callbacks.c
new file mode 100644
index 000000000000..32d9b8d17964
--- /dev/null
+++ b/fs/read_callbacks.c
@@ -0,0 +1,285 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * This file tracks the state machine that needs to be executed after reading
+ * data from files that are encrypted and/or have verity metadata associated
+ * with them.
+ */
+#include <linux/module.h>
+#include <linux/mm.h>
+#include <linux/pagemap.h>
+#include <linux/bio.h>
+#include <linux/buffer_head.h>
+#include <linux/fscrypt.h>
+#include <linux/read_callbacks.h>
+#include <linux/blk_types.h>
+
+#define NUM_PREALLOC_READ_CALLBACK_CTXS	128
+
+static struct kmem_cache *read_callbacks_ctx_cache;
+static mempool_t *read_callbacks_ctx_pool;
+
+/* Read callback state machine steps */
+enum read_callbacks_step {
+	STEP_INITIAL = 0,
+	STEP_DECRYPT,
+};
+
+struct read_callbacks_ctx {
+	struct inode *inode;
+	struct bio *bio;
+	struct buffer_head *bh;
+	union {
+		end_bio_func_t end_bio;
+
+		struct {
+			end_bh_func_t end_bh;
+			int bh_uptodate;
+		};
+	};
+	struct work_struct work;
+	unsigned int enabled_steps;
+	enum read_callbacks_step cur_step;
+};
+
+static void read_callbacks(struct read_callbacks_ctx *ctx);
+
+static void free_read_callbacks_ctx(struct read_callbacks_ctx *ctx)
+{
+	mempool_free(ctx, read_callbacks_ctx_pool);
+}
+
+static struct read_callbacks_ctx *get_read_callbacks_ctx(struct inode *inode)
+{
+	struct read_callbacks_ctx *ctx = NULL;
+	unsigned int enabled_steps = 0;
+
+	if (IS_ENCRYPTED(inode) && S_ISREG(inode->i_mode))
+		enabled_steps |= 1 << STEP_DECRYPT;
+
+	if (enabled_steps) {
+		ctx = mempool_alloc(read_callbacks_ctx_pool, GFP_NOFS);
+		if (!ctx)
+			return ERR_PTR(-ENOMEM);
+
+		ctx->inode = inode;
+		ctx->enabled_steps = enabled_steps;
+		ctx->cur_step = STEP_INITIAL;
+	}
+
+	return ctx;
+}
+
+static void decrypt_bio(struct bio *bio)
+{
+	struct bio_vec *bv;
+	int i;
+	struct bvec_iter_all iter_all;
+
+	bio_for_each_segment_all(bv, bio, i, iter_all) {
+		struct page *page = bv->bv_page;
+		int ret = fscrypt_decrypt_pagecache_blocks(page, bv->bv_len,
+							   bv->bv_offset);
+		if (ret)
+			SetPageError(page);
+	}
+}
+
+static void decrypt_bh(struct buffer_head *bh)
+{
+	struct page *page;
+	int ret;
+
+	page = bh->b_page;
+
+	ret = fscrypt_decrypt_pagecache_blocks(page, bh->b_size,
+					bh_offset(bh));
+	if (ret)
+		SetPageError(page);
+}
+
+static void decrypt_work(struct work_struct *work)
+{
+	struct read_callbacks_ctx *ctx =
+		container_of(work, struct read_callbacks_ctx, work);
+
+	if (ctx->bio)
+		decrypt_bio(ctx->bio);
+	else
+		decrypt_bh(ctx->bh);
+
+	read_callbacks(ctx);
+}
+
+static void read_callbacks(struct read_callbacks_ctx *ctx)
+{
+	/*
+	 * We use different work queues for decryption and for verity because
+	 * verity may require reading metadata pages that need decryption, and
+	 * we shouldn't recurse to the same workqueue.
+	 */
+	switch (++ctx->cur_step) {
+	case STEP_DECRYPT:
+		if (ctx->enabled_steps & (1 << STEP_DECRYPT)) {
+			INIT_WORK(&ctx->work, decrypt_work);
+			fscrypt_enqueue_decrypt_work(&ctx->work);
+			return;
+		}
+		ctx->cur_step++;
+		/* fall-through */
+	default:
+		if (ctx->bio)
+			ctx->end_bio(ctx->bio);
+		else
+			ctx->end_bh(ctx->bh, ctx->bh_uptodate);
+
+		mempool_free(ctx, read_callbacks_ctx_pool);
+	}
+}
+
+/**
+ * read_callbacks_setup_bio() - Initialize the read callbacks state machine
+ * @inode: The file on which read I/O is performed.
+ * @bio: bio holding page cache pages on which read I/O is performed.
+ * @bh: Buffer head on which read I/O is performed.
+ * @page_op: Function to perform filesystem specific operations on a page.
+ *
+ * Based on the nature of the file's data (e.g. encrypted), this function
+ * computes the steps that need to be performed after data is read of the
+ * backing disk. This information is saved in a context structure. A pointer
+ * to the context structure is then stored in bio->bi_private for later
+ * usage.
+ *
+ * Return: 0 on success; An error code on failure.
+ */
+int read_callbacks_setup_bio(struct inode *inode, struct bio *bio)
+{
+	struct read_callbacks_ctx *ctx = get_read_callbacks_ctx(inode);
+
+	if (ctx) {
+		if (IS_ERR(ctx))
+			return PTR_ERR(ctx);
+		ctx->bio = bio;
+		ctx->bh = NULL;
+		bio->bi_private = ctx;
+	}
+
+	return 0;
+}
+EXPORT_SYMBOL(read_callbacks_setup_bio);
+
+/**
+ * read_callbacks_setup_bh() - Initialize the read callbacks state machine
+ * @inode: The file on which read I/O is performed.
+ * @bio: bio holding page cache pages on which read I/O is performed.
+ * @bh: Buffer head on which read I/O is performed.
+ * @page_op: Function to perform filesystem specific operations on a page.
+ *
+ * Based on the nature of the file's data (e.g. encrypted), this function
+ * computes the steps that need to be performed after data is read of the
+ * backing disk. This information is saved in a context structure. A pointer
+ * to the context structure is then stored in bio->bi_private for later
+ * usage.
+ *
+ * Return: 0 on success; An error code on failure.
+ */
+int read_callbacks_setup_bh(struct inode *inode, struct buffer_head *bh)
+{
+	struct read_callbacks_ctx *ctx = get_read_callbacks_ctx(inode);
+
+	if (ctx) {
+		if (IS_ERR(ctx))
+			return PTR_ERR(ctx);
+		ctx->bio = NULL;
+		ctx->bh = bh;
+		bh->b_private = ctx;
+		set_buffer_read_cb(bh);
+	}
+
+	return 0;
+}
+EXPORT_SYMBOL(read_callbacks_setup_bh);
+
+/**
+ * read_callbacks_endio_bio() - Initiate the read callbacks state machine.
+ * @bio: bio on which read I/O operation has just been completed.
+ * @end_bio: Callback to invoke on @bio after state machine completion.
+ *
+ * Initiates the execution of the read callbacks state machine when the read
+ * operation has been completed sucessfully. If there was an error associated
+ * with the bio, this function frees the read callbacks context structure stored
+ * in bio->bi_private (if any).
+ *
+ * If read callbacks state machine isn't executed, we end up invoking the
+ * @end_bio function passed in as an argument.
+ */
+void read_callbacks_endio_bio(struct bio *bio, end_bio_func_t end_bio)
+{
+	struct read_callbacks_ctx *ctx = bio->bi_private;
+
+	if (ctx) {
+		if (!bio->bi_status) {
+			ctx->end_bio = end_bio;
+			read_callbacks(ctx);
+			return;
+		}
+
+		free_read_callbacks_ctx(ctx);
+	}
+
+	end_bio(bio);
+}
+EXPORT_SYMBOL(read_callbacks_endio_bio);
+
+/**
+ * read_callbacks_endio_bh() - Initiate the read callbacks state machine.
+ * @bh: buffer head on which read I/O operation has just been completed.
+ * @uptodate: Buffer head's I/O status.
+ * @end_bh: Callback to invoke on on @bh after state machine completion.
+ *
+ * Initiates the execution of the read callbacks state machine when the read
+ * operation has been completed sucessfully. If there was an error associated
+ * with the buffer head, this function frees the read callbacks context
+ * structure stored in bh->b_private (if any).
+ *
+ * If read callbacks state machine isn't executed, we end up invoking the
+ * @end_bh function passed in as an argument.
+ */
+void read_callbacks_endio_bh(struct buffer_head *bh, int uptodate, end_bh_func_t end_bh)
+{
+	struct read_callbacks_ctx *ctx = bh->b_private;
+
+	if (buffer_read_cb(bh)) {
+		clear_buffer_read_cb(bh);
+		if (uptodate) {
+			ctx->end_bh = end_bh;
+			ctx->bh_uptodate = uptodate;
+			read_callbacks(ctx);
+			return;
+		}
+
+		free_read_callbacks_ctx(ctx);
+	}
+
+	end_bh(bh, uptodate);
+}
+EXPORT_SYMBOL(read_callbacks_endio_bh);
+
+static int __init init_read_callbacks(void)
+{
+	read_callbacks_ctx_cache = KMEM_CACHE(read_callbacks_ctx, 0);
+	if (!read_callbacks_ctx_cache)
+		goto fail;
+	read_callbacks_ctx_pool =
+		mempool_create_slab_pool(NUM_PREALLOC_READ_CALLBACK_CTXS,
+					 read_callbacks_ctx_cache);
+	if (!read_callbacks_ctx_pool)
+		goto fail_free_cache;
+	return 0;
+
+fail_free_cache:
+	kmem_cache_destroy(read_callbacks_ctx_cache);
+fail:
+	return -ENOMEM;
+}
+
+fs_initcall(init_read_callbacks);
diff --git a/include/linux/read_callbacks.h b/include/linux/read_callbacks.h
new file mode 100644
index 000000000000..0d709dd81b4e
--- /dev/null
+++ b/include/linux/read_callbacks.h
@@ -0,0 +1,48 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef _READ_CALLBACKS_H
+#define _READ_CALLBACKS_H
+
+#include <linux/blk_types.h>
+
+typedef void (*end_bio_func_t)(struct bio *bio);
+typedef void (*end_bh_func_t)(struct buffer_head *bh, int uptodate);
+
+#ifdef CONFIG_FS_READ_CALLBACKS
+int read_callbacks_setup_bio(struct inode *inode, struct bio *bio);
+int read_callbacks_setup_bh(struct inode *inode, struct buffer_head *bh);
+void read_callbacks_endio_bio(struct bio *bio, end_bio_func_t end_bio);
+void read_callbacks_endio_bh(struct buffer_head *bh, int uptodate, end_bh_func_t end_bh);
+
+static inline bool read_callbacks_failed(struct page *page)
+{
+	return PageError(page);
+}
+#else
+static inline int read_callbacks_setup_bio(struct inode *inode, struct bio *bio)
+{
+	return 0;
+}
+
+static inline int read_callbacks_setup_bh(struct inode *inode, struct buffer_head *bh)
+{
+	return 0;
+}
+
+static inline void read_callbacks_endio_bio(struct bio *bio,
+					end_bio_func_t end_bio)
+{
+	end_bio(bio);
+}
+
+static inline void read_callbacks_endio_bh(struct buffer_head *bh, int uptodate, end_bh_func_t end_bh)
+{
+	end_bh(bh, uptodate);
+}
+
+static inline bool read_callbacks_failed(struct page *page)
+{
+	return false;
+}
+#endif
+
+#endif	/* _READ_CALLBACKS_H */
-- 
2.19.1

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