[PATCH v10 07/21] Replace XIP read and write with DAX I/O

Matthew Wilcox
2014-08-27T04:40:19Z

Use the generic AIO infrastructure instead of custom read and write
methods. In addition to giving us support for AIO, this adds the missing
locking between read() and truncate().

Signed-off-by: Matthew Wilcox <matthew.r.wilcox@intel.com>
Reviewed-by: Ross Zwisler <ross.zwisler@linux.intel.com>
Reviewed-by: Jan Kara <jack@suse.cz>
---
MAINTAINERS | 6 ++
fs/Makefile | 1 +
fs/dax.c | 195 ++++++++++++++++++++++++++++++++++++++++++++
fs/ext2/file.c | 6 +-
fs/ext2/inode.c | 8 +-
include/linux/fs.h | 18 ++++-
mm/filemap.c | 6 +-
mm/filemap_xip.c | 234 -----------------------------------------------------
8 files changed, 229 insertions(+), 245 deletions(-)
create mode 100644 fs/dax.c

diff --git a/MAINTAINERS b/MAINTAINERS
index 1ff06de..3f29153 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -2929,6 +2929,12 @@ L: linux-i2c@vger.kernel.org
S: Maintained
F: drivers/i2c/busses/i2c-diolan-u2c.c

+DIRECT ACCESS (DAX)
+M: Matthew Wilcox <willy@linux.intel.com>
+L: linux-fsdevel@vger.kernel.org
+S: Supported
+F: fs/dax.c
+
DIRECTORY NOTIFICATION (DNOTIFY)
M: Eric Paris <eparis@parisplace.org>
S: Maintained
diff --git a/fs/Makefile b/fs/Makefile
index 90c8852..0325ec3 100644
--- a/fs/Makefile
+++ b/fs/Makefile
@@ -28,6 +28,7 @@ obj-$(CONFIG_SIGNALFD) += signalfd.o
obj-$(CONFIG_TIMERFD) += timerfd.o
obj-$(CONFIG_EVENTFD) += eventfd.o
obj-$(CONFIG_AIO) += aio.o
+obj-$(CONFIG_FS_XIP) += dax.o
obj-$(CONFIG_FILE_LOCKING) += locks.o
obj-$(CONFIG_COMPAT) += compat.o compat_ioctl.o
obj-$(CONFIG_BINFMT_AOUT) += binfmt_aout.o
diff --git a/fs/dax.c b/fs/dax.c
new file mode 100644
index 0000000..108c68e
--- /dev/null
+++ b/fs/dax.c
@@ -0,0 +1,195 @@
+/*
+ * fs/dax.c - Direct Access filesystem code
+ * Copyright (c) 2013-2014 Intel Corporation
+ * Author: Matthew Wilcox <matthew.r.wilcox@intel.com>
+ * Author: Ross Zwisler <ross.zwisler@linux.intel.com>
+ *
+ * This program is free software; you can redistribute it and/or modify it
+ * under the terms and conditions of the GNU General Public License,
+ * version 2, as published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for
+ * more details.
+ */
+
+#include <linux/atomic.h>
+#include <linux/blkdev.h>
+#include <linux/buffer_head.h>
+#include <linux/fs.h>
+#include <linux/genhd.h>
+#include <linux/mutex.h>
+#include <linux/uio.h>
+
+static long dax_get_addr(struct buffer_head *bh, void **addr, unsigned blkbits)
+{
+ unsigned long pfn;
+ sector_t sector = bh->b_blocknr << (blkbits - 9);
+ return bdev_direct_access(bh->b_bdev, sector, addr, &pfn, bh->b_size);
+}
+
+static void dax_new_buf(void *addr, unsigned size, unsigned first, loff_t pos,
+ loff_t end)
+{
+ loff_t final = end - pos + first; /* The final byte of the buffer */
+
+ if (first > 0)
+ memset(addr, 0, first);
+ if (final < size)
+ memset(addr + final, 0, size - final);
+}
+
+static bool buffer_written(struct buffer_head *bh)
+{
+ return buffer_mapped(bh) && !buffer_unwritten(bh);
+}
+
+/*
+ * When ext4 encounters a hole, it returns without modifying the buffer_head
+ * which means that we can't trust b_size. To cope with this, we set b_state
+ * to 0 before calling get_block and, if any bit is set, we know we can trust
+ * b_size. Unfortunate, really, since ext4 knows precisely how long a hole is
+ * and would save us time calling get_block repeatedly.
+ */
+static bool buffer_size_valid(struct buffer_head *bh)
+{
+ return bh->b_state != 0;
+}
+
+static ssize_t dax_io(int rw, struct inode *inode, struct iov_iter *iter,
+ loff_t start, loff_t end, get_block_t get_block,
+ struct buffer_head *bh)
+{
+ ssize_t retval = 0;
+ loff_t pos = start;
+ loff_t max = start;
+ loff_t bh_max = start;
+ void *addr;
+ bool hole = false;
+
+ if (rw != WRITE)
+ end = min(end, i_size_read(inode));
+
+ while (pos < end) {
+ unsigned len;
+ if (pos == max) {
+ unsigned blkbits = inode->i_blkbits;
+ sector_t block = pos >> blkbits;
+ unsigned first = pos - (block << blkbits);
+ long size;
+
+ if (pos == bh_max) {
+ bh->b_size = PAGE_ALIGN(end - pos);
+ bh->b_state = 0;
+ retval = get_block(inode, block, bh,
+ rw == WRITE);
+ if (retval)
+ break;
+ if (!buffer_size_valid(bh))
+ bh->b_size = 1 << blkbits;
+ bh_max = pos - first + bh->b_size;
+ } else {
+ unsigned done = bh->b_size -
+ (bh_max - (pos - first));
+ bh->b_blocknr += done >> blkbits;
+ bh->b_size -= done;
+ }
+ if (rw == WRITE) {
+ if (!buffer_mapped(bh)) {
+ retval = -EIO;
+ /* FIXME: fall back to buffered I/O */
+ break;
+ }
+ hole = false;
+ } else {
+ hole = !buffer_written(bh);
+ }
+
+ if (hole) {
+ addr = NULL;
+ size = bh->b_size - first;
+ } else {
+ retval = dax_get_addr(bh, &addr, blkbits);
+ if (retval < 0)
+ break;
+ if (buffer_unwritten(bh) || buffer_new(bh))
+ dax_new_buf(addr, retval, first, pos,
+ end);
+ addr += first;
+ size = retval - first;
+ }
+ max = min(pos + size, end);
+ }
+
+ if (rw == WRITE)
+ len = copy_from_iter(addr, max - pos, iter);
+ else if (!hole)
+ len = copy_to_iter(addr, max - pos, iter);
+ else
+ len = iov_iter_zero(max - pos, iter);
+
+ if (!len)
+ break;
+
+ pos += len;
+ addr += len;
+ }
+
+ return (pos == start) ? retval : pos - start;
+}
+
+/**
+ * dax_do_io - Perform I/O to a DAX file
+ * @rw: READ to read or WRITE to write
+ * @iocb: The control block for this I/O
+ * @inode: The file which the I/O is directed at
+ * @iter: The addresses to do I/O from or to
+ * @pos: The file offset where the I/O starts
+ * @get_block: The filesystem method used to translate file offsets to blocks
+ * @end_io: A filesystem callback for I/O completion
+ * @flags: See below
+ *
+ * This function uses the same locking scheme as do_blockdev_direct_IO:
+ * If @flags has DIO_LOCKING set, we assume that the i_mutex is held by the
+ * caller for writes. For reads, we take and release the i_mutex ourselves.
+ * If DIO_LOCKING is not set, the filesystem takes care of its own locking.
+ * As with do_blockdev_direct_IO(), we increment i_dio_count while the I/O
+ * is in progress.
+ */
+ssize_t dax_do_io(int rw, struct kiocb *iocb, struct inode *inode,
+ struct iov_iter *iter, loff_t pos,
+ get_block_t get_block, dio_iodone_t end_io, int flags)
+{
+ struct buffer_head bh;
+ ssize_t retval = -EINVAL;
+ loff_t end = pos + iov_iter_count(iter);
+
+ memset(&bh, 0, sizeof(bh));
+
+ if ((flags & DIO_LOCKING) && (rw == READ)) {
+ struct address_space *mapping = inode->i_mapping;
+ mutex_lock(&inode->i_mutex);
+ retval = filemap_write_and_wait_range(mapping, pos, end - 1);
+ if (retval) {
+ mutex_unlock(&inode->i_mutex);
+ goto out;
+ }
+ }
+
+ /* Protects against truncate */
+ atomic_inc(&inode->i_dio_count);
+
+ retval = dax_io(rw, inode, iter, pos, end, get_block, &bh);
+
+ if ((flags & DIO_LOCKING) && (rw == READ))
+ mutex_unlock(&inode->i_mutex);
+
+ if ((retval > 0) && end_io)
+ end_io(iocb, pos, retval, bh.b_private);
+
+ inode_dio_done(inode);
+ out:
+ return retval;
+}
+EXPORT_SYMBOL_GPL(dax_do_io);
diff --git a/fs/ext2/file.c b/fs/ext2/file.c
index 7c87b22..a247123 100644
--- a/fs/ext2/file.c
+++ b/fs/ext2/file.c
@@ -81,8 +81,10 @@ const struct file_operations ext2_file_operations = {
#ifdef CONFIG_EXT2_FS_XIP
const struct file_operations ext2_xip_file_operations = {
.llseek = generic_file_llseek,
- .read = xip_file_read,
- .write = xip_file_write,
+ .read = new_sync_read,
+ .write = new_sync_write,
+ .read_iter = generic_file_read_iter,
+ .write_iter = generic_file_write_iter,
.unlocked_ioctl = ext2_ioctl,
#ifdef CONFIG_COMPAT
.compat_ioctl = ext2_compat_ioctl,
diff --git a/fs/ext2/inode.c b/fs/ext2/inode.c
index 0cb0448..3ccd5fd 100644
--- a/fs/ext2/inode.c
+++ b/fs/ext2/inode.c
@@ -859,7 +859,12 @@ ext2_direct_IO(int rw, struct kiocb *iocb, struct iov_iter *iter,
size_t count = iov_iter_count(iter);
ssize_t ret;

- ret = blockdev_direct_IO(rw, iocb, inode, iter, offset, ext2_get_block);
+ if (IS_DAX(inode))
+ ret = dax_do_io(rw, iocb, inode, iter, offset, ext2_get_block,
+ NULL, DIO_LOCKING);
+ else
+ ret = blockdev_direct_IO(rw, iocb, inode, iter, offset,
+ ext2_get_block);
if (ret < 0 && (rw & WRITE))
ext2_write_failed(mapping, offset + count);
return ret;
@@ -888,6 +893,7 @@ const struct address_space_operations ext2_aops = {
const struct address_space_operations ext2_aops_xip = {
.bmap = ext2_bmap,
.get_xip_mem = ext2_get_xip_mem,
+ .direct_IO = ext2_direct_IO,
};

const struct address_space_operations ext2_nobh_aops = {
diff --git a/include/linux/fs.h b/include/linux/fs.h
index e99e5c4..45839e8 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -2490,17 +2490,22 @@ extern int generic_file_open(struct inode * inode, struct file * filp);
extern int nonseekable_open(struct inode * inode, struct file * filp);

#ifdef CONFIG_FS_XIP
-extern ssize_t xip_file_read(struct file *filp, char __user *buf, size_t len,
- loff_t *ppos);
extern int xip_file_mmap(struct file * file, struct vm_area_struct * vma);
-extern ssize_t xip_file_write(struct file *filp, const char __user *buf,
- size_t len, loff_t *ppos);
extern int xip_truncate_page(struct address_space *mapping, loff_t from);
+ssize_t dax_do_io(int rw, struct kiocb *, struct inode *, struct iov_iter *,
+ loff_t, get_block_t, dio_iodone_t, int flags);
#else
static inline int xip_truncate_page(struct address_space *mapping, loff_t from)
{
return 0;
}
+
+static inline ssize_t dax_do_io(int rw, struct kiocb *iocb,
+ struct inode *inode, struct iov_iter *iter, loff_t pos,
+ get_block_t get_block, dio_iodone_t end_io, int flags)
+{
+ return -ENOTTY;
+}
#endif

#ifdef CONFIG_BLOCK
@@ -2657,6 +2662,11 @@ extern int generic_show_options(struct seq_file *m, struct dentry *root);
extern void save_mount_options(struct super_block *sb, char *options);
extern void replace_mount_options(struct super_block *sb, char *options);

+static inline bool io_is_direct(struct file *filp)
+{
+ return (filp->f_flags & O_DIRECT) || IS_DAX(file_inode(filp));
+}
+
static inline ino_t parent_ino(struct dentry *dentry)
{
ino_t res;
diff --git a/mm/filemap.c b/mm/filemap.c
index 90effcd..19bdb68 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -1690,8 +1690,7 @@ generic_file_read_iter(struct kiocb *iocb, struct iov_iter *iter)
loff_t *ppos = &iocb->ki_pos;
loff_t pos = *ppos;

- /* coalesce the iovecs and go direct-to-BIO for O_DIRECT */
- if (file->f_flags & O_DIRECT) {
+ if (io_is_direct(file)) {
struct address_space *mapping = file->f_mapping;
struct inode *inode = mapping->host;
size_t count = iov_iter_count(iter);
@@ -2579,8 +2578,7 @@ ssize_t __generic_file_write_iter(struct kiocb *iocb, struct iov_iter *from)
if (err)
goto out;

- /* coalesce the iovecs and go direct-to-BIO for O_DIRECT */
- if (unlikely(file->f_flags & O_DIRECT)) {
+ if (io_is_direct(file)) {
loff_t endbyte;

written = generic_file_direct_write(iocb, from, pos);
diff --git a/mm/filemap_xip.c b/mm/filemap_xip.c
index c8d23e9..f7c37a1 100644
--- a/mm/filemap_xip.c
+++ b/mm/filemap_xip.c
@@ -42,119 +42,6 @@ static struct page *xip_sparse_page(void)
}

/*
- * This is a file read routine for execute in place files, and uses
- * the mapping->a_ops->get_xip_mem() function for the actual low-level
- * stuff.
- *
- * Note the struct file* is not used at all. It may be NULL.
- */
-static ssize_t
-do_xip_mapping_read(struct address_space *mapping,
- struct file_ra_state *_ra,
- struct file *filp,
- char __user *buf,
- size_t len,
- loff_t *ppos)
-{
- struct inode *inode = mapping->host;
- pgoff_t index, end_index;
- unsigned long offset;
- loff_t isize, pos;
- size_t copied = 0, error = 0;
-
- BUG_ON(!mapping->a_ops->get_xip_mem);
-
- pos = *ppos;
- index = pos >> PAGE_CACHE_SHIFT;
- offset = pos & ~PAGE_CACHE_MASK;
-
- isize = i_size_read(inode);
- if (!isize)
- goto out;
-
- end_index = (isize - 1) >> PAGE_CACHE_SHIFT;
- do {
- unsigned long nr, left;
- void *xip_mem;
- unsigned long xip_pfn;
- int zero = 0;
-
- /* nr is the maximum number of bytes to copy from this page */
- nr = PAGE_CACHE_SIZE;
- if (index >= end_index) {
- if (index > end_index)
- goto out;
- nr = ((isize - 1) & ~PAGE_CACHE_MASK) + 1;
- if (nr <= offset) {
- goto out;
- }
- }
- nr = nr - offset;
- if (nr > len - copied)
- nr = len - copied;
-
- error = mapping->a_ops->get_xip_mem(mapping, index, 0,
- &xip_mem, &xip_pfn);
- if (unlikely(error)) {
- if (error == -ENODATA) {
- /* sparse */
- zero = 1;
- } else
- goto out;
- }
-
- /* If users can be writing to this page using arbitrary
- * virtual addresses, take care about potential aliasing
- * before reading the page on the kernel side.
- */
- if (mapping_writably_mapped(mapping))
- /* address based flush */ ;
-
- /*
- * Ok, we have the mem, so now we can copy it to user space...
- *
- * The actor routine returns how many bytes were actually used..
- * NOTE! This may not be the same as how much of a user buffer
- * we filled up (we may be padding etc), so we can only update
- * "pos" here (the actor routine has to update the user buffer
- * pointers and the remaining count).
- */
- if (!zero)
- left = __copy_to_user(buf+copied, xip_mem+offset, nr);
- else
- left = __clear_user(buf + copied, nr);
-
- if (left) {
- error = -EFAULT;
- goto out;
- }
-
- copied += (nr - left);
- offset += (nr - left);
- index += offset >> PAGE_CACHE_SHIFT;
- offset &= ~PAGE_CACHE_MASK;
- } while (copied < len);
-
-out:
- *ppos = pos + copied;
- if (filp)
- file_accessed(filp);
-
- return (copied ? copied : error);
-}
-
-ssize_t
-xip_file_read(struct file *filp, char __user *buf, size_t len, loff_t *ppos)
-{
- if (!access_ok(VERIFY_WRITE, buf, len))
- return -EFAULT;
-
- return do_xip_mapping_read(filp->f_mapping, &filp->f_ra, filp,
- buf, len, ppos);
-}
-EXPORT_SYMBOL_GPL(xip_file_read);
-
-/*
* __xip_unmap is invoked from xip_unmap and
* xip_write
*
@@ -340,127 +227,6 @@ int xip_file_mmap(struct file * file, struct vm_area_struct * vma)
}
EXPORT_SYMBOL_GPL(xip_file_mmap);

-static ssize_t
-__xip_file_write(struct file *filp, const char __user *buf,
- size_t count, loff_t pos, loff_t *ppos)
-{
- struct address_space * mapping = filp->f_mapping;
- const struct address_space_operations *a_ops = mapping->a_ops;
- struct inode *inode = mapping->host;
- long status = 0;
- size_t bytes;
- ssize_t written = 0;
-
- BUG_ON(!mapping->a_ops->get_xip_mem);
-
- do {
- unsigned long index;
- unsigned long offset;
- size_t copied;
- void *xip_mem;
- unsigned long xip_pfn;
-
- offset = (pos & (PAGE_CACHE_SIZE -1)); /* Within page */
- index = pos >> PAGE_CACHE_SHIFT;
- bytes = PAGE_CACHE_SIZE - offset;
- if (bytes > count)
- bytes = count;
-
- status = a_ops->get_xip_mem(mapping, index, 0,
- &xip_mem, &xip_pfn);
- if (status == -ENODATA) {
- /* we allocate a new page unmap it */
- mutex_lock(&xip_sparse_mutex);
- status = a_ops->get_xip_mem(mapping, index, 1,
- &xip_mem, &xip_pfn);
- mutex_unlock(&xip_sparse_mutex);
- if (!status)
- /* unmap page at pgoff from all other vmas */
- __xip_unmap(mapping, index);
- }
-
- if (status)
- break;
-
- copied = bytes -
- __copy_from_user_nocache(xip_mem + offset, buf, bytes);
-
- if (likely(copied > 0)) {
- status = copied;
-
- if (status >= 0) {
- written += status;
- count -= status;
- pos += status;
- buf += status;
- }
- }
- if (unlikely(copied != bytes))
- if (status >= 0)
- status = -EFAULT;
- if (status < 0)
- break;
- } while (count);
- *ppos = pos;
- /*
- * No need to use i_size_read() here, the i_size
- * cannot change under us because we hold i_mutex.
- */
- if (pos > inode->i_size) {
- i_size_write(inode, pos);
- mark_inode_dirty(inode);
- }
-
- return written ? written : status;
-}
-
-ssize_t
-xip_file_write(struct file *filp, const char __user *buf, size_t len,
- loff_t *ppos)
-{
- struct address_space *mapping = filp->f_mapping;
- struct inode *inode = mapping->host;
- size_t count;
- loff_t pos;
- ssize_t ret;
-
- mutex_lock(&inode->i_mutex);
-
- if (!access_ok(VERIFY_READ, buf, len)) {
- ret=-EFAULT;
- goto out_up;
- }
-
- pos = *ppos;
- count = len;
-
- /* We can write back this queue in page reclaim */
- current->backing_dev_info = mapping->backing_dev_info;
-
- ret = generic_write_checks(filp, &pos, &count, S_ISBLK(inode->i_mode));
- if (ret)
- goto out_backing;
- if (count == 0)
- goto out_backing;
-
- ret = file_remove_suid(filp);
- if (ret)
- goto out_backing;
-
- ret = file_update_time(filp);
- if (ret)
- goto out_backing;
-
- ret = __xip_file_write (filp, buf, count, pos, ppos);
-
- out_backing:
- current->backing_dev_info = NULL;
- out_up:
- mutex_unlock(&inode->i_mutex);
- return ret;
-}
-EXPORT_SYMBOL_GPL(xip_file_write);
-
/*
* truncate a page used for execute in place
* functionality is analog to block_truncate_page but does use get_xip_mem
--
2.0.0