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Message-ID: <20131219010530.GA17545@parisc-linux.org>
Date: Wed, 18 Dec 2013 18:05:31 -0700
From: Matthew Wilcox <matthew@....cx>
To: Dave Chinner <david@...morbit.com>
Cc: Matthew Wilcox <matthew.r.wilcox@...el.com>,
linux-ext4@...r.kernel.org, linux-fsdevel@...r.kernel.org
Subject: Re: [PATCH v3 0/3] Add XIP support to ext4
On Thu, Dec 19, 2013 at 11:48:31AM +1100, Dave Chinner wrote:
> We already have a model for handling non page cache based IO paths:
> Direct IO has to handle this read/truncate race condition without
> page lock serialisation, and it works just fine. Go and look at
> inode_dio_wait() rather than reinventing the wheel.
I've spent most of today looking at that code. Here's where I'm at
right now. It doesn't even compile.
diff --git a/fs/ext2/xip.h b/fs/ext2/xip.h
index 18b34d2..29be737 100644
--- a/fs/ext2/xip.h
+++ b/fs/ext2/xip.h
@@ -16,9 +16,7 @@ static inline int ext2_use_xip (struct super_block *sb)
}
int ext2_get_xip_mem(struct address_space *, pgoff_t, int,
void **, unsigned long *);
-#define mapping_is_xip(map) unlikely(map->a_ops->get_xip_mem)
#else
-#define mapping_is_xip(map) 0
#define ext2_xip_verify_sb(sb) do { } while (0)
#define ext2_use_xip(sb) 0
#define ext2_clear_xip_target(inode, chain) 0
diff --git a/fs/ext4/file.c b/fs/ext4/file.c
index b9499b2..66d2b35 100644
--- a/fs/ext4/file.c
+++ b/fs/ext4/file.c
@@ -190,7 +190,8 @@ ext4_file_write(struct kiocb *iocb, const struct iovec *iov,
}
}
- if (unlikely(iocb->ki_filp->f_flags & O_DIRECT))
+ if (unlikely(iocb->ki_filp->f_flags & O_DIRECT) ||
+ (mapping_is_xip(inode->i_mapping)))
ret = ext4_file_dio_write(iocb, iov, nr_segs, pos);
else
ret = generic_file_aio_write(iocb, iov, nr_segs, pos);
@@ -612,8 +613,10 @@ const struct file_operations ext4_file_operations = {
#ifdef CONFIG_EXT4_FS_XIP
const struct file_operations ext4_xip_file_operations = {
.llseek = ext4_llseek,
- .read = xip_file_read,
- .write = xip_file_write,
+ .read = do_sync_read,
+ .write = do_sync_write,
+ .aio_read = generic_file_aio_read,
+ .aio_write = ext4_file_write,
.unlocked_ioctl = ext4_ioctl,
#ifdef CONFIG_COMPAT
.compat_ioctl = ext4_compat_ioctl,
diff --git a/fs/ext4/indirect.c b/fs/ext4/indirect.c
index 594009f..ae760d9 100644
--- a/fs/ext4/indirect.c
+++ b/fs/ext4/indirect.c
@@ -686,15 +686,22 @@ retry:
inode_dio_done(inode);
goto locked;
}
- ret = __blockdev_direct_IO(rw, iocb, inode,
- inode->i_sb->s_bdev, iov,
- offset, nr_segs,
- ext4_get_block, NULL, NULL, 0);
+ if (mapping_is_xip(file->f_mapping))
+ ret = xip_io(rw, iocb, inode, iov, offset, nr_segs,
+ ext4_get_block, NULL, 0);
+ else
+ ret = __blockdev_direct_IO(rw, iocb, inode,
+ inode->i_sb->s_bdev, iov, offset,
+ nr_segs, ext4_get_block, NULL, NULL, 0);
inode_dio_done(inode);
} else {
locked:
- ret = blockdev_direct_IO(rw, iocb, inode, iov,
- offset, nr_segs, ext4_get_block);
+ if (mapping_is_xip(file->f_mapping))
+ ret = xip_io(rw, iocb, inode, iov, offset, nr_segs,
+ ext4_get_block, NULL, 0);
+ else
+ ret = blockdev_direct_IO(rw, iocb, inode, iov,
+ offset, nr_segs, ext4_get_block);
if (unlikely((rw & WRITE) && ret < 0)) {
loff_t isize = i_size_read(inode);
diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
index 7b50832..0303412 100644
--- a/fs/ext4/inode.c
+++ b/fs/ext4/inode.c
@@ -3170,13 +3170,14 @@ static ssize_t ext4_ext_direct_IO(int rw, struct kiocb *iocb,
get_block_func = ext4_get_block_write;
dio_flags = DIO_LOCKING;
}
- ret = __blockdev_direct_IO(rw, iocb, inode,
- inode->i_sb->s_bdev, iov,
- offset, nr_segs,
- get_block_func,
- ext4_end_io_dio,
- NULL,
- dio_flags);
+ if (mapping_is_xip(file->f_mapping))
+ ret = xip_io(rw, iocb, inode, iov, offset, nr_segs,
+ get_block_func, ext4_end_io_dio, dio_flags);
+ else
+ ret = __blockdev_direct_IO(rw, iocb, inode,
+ inode->i_sb->s_bdev, iov, offset,
+ nr_segs, get_block_func,
+ ext4_end_io_dio, NULL, dio_flags);
/*
* Put our reference to io_end. This can free the io_end structure e.g.
@@ -3291,6 +3292,7 @@ static const struct address_space_operations ext4_aops = {
const struct address_space_operations ext4_xip_aops = {
.bmap = ext4_bmap,
.get_xip_mem = ext4_get_xip_mem,
+ .direct_IO = ext4_direct_IO,
};
static const struct address_space_operations ext4_journalled_aops = {
diff --git a/fs/ext4/xip.h b/fs/ext4/xip.h
index af0d553..b279dae 100644
--- a/fs/ext4/xip.h
+++ b/fs/ext4/xip.h
@@ -15,9 +15,7 @@ static inline int ext4_use_xip(struct super_block *sb)
}
int ext4_get_xip_mem(struct address_space *, pgoff_t, int,
void **, unsigned long *);
-#define mapping_is_xip(map) unlikely(map->a_ops->get_xip_mem)
#else
-#define mapping_is_xip(map) 0
#define ext4_use_xip(sb) 0
#define ext4_clear_xip_target(inode, chain) 0
#define ext4_get_xip_mem NULL
diff --git a/include/linux/fs.h b/include/linux/fs.h
index a063bff..94a8e50 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -2511,6 +2511,14 @@ extern ssize_t xip_file_write(struct file *filp, const char __user *buf,
extern int xip_truncate_page(struct address_space *mapping, loff_t from);
extern int xip_zero_page_range(struct address_space *, loff_t from,
unsigned length);
+extern ssize_t xip_io(int rw, struct kiocb *, struct inode *,
+ const struct iovec *, loff_t, unsigned segs,
+ get_block_t, dio_iodone_t, int flags);
+
+static inline bool mapping_is_xip(struct address_space *mapping)
+{
+ return mapping->a_ops->get_xip_mem != NULL;
+}
#else
static inline int xip_truncate_page(struct address_space *mapping, loff_t from)
{
@@ -2522,6 +2530,18 @@ static inline int xip_zero_page_range(struct address_space *mapping,
{
return 0;
}
+
+static inline bool mapping_is_xip(struct address_space *mapping)
+{
+ return false;
+}
+
+static inline ssize_t xip_io(int rw, struct kiocb *iocb, struct inode *inode,
+ const struct iovec *iov, loff_t offset, unsigned nr_segs,
+ get_block_t get_block, dio_iodone_t end_io, int flags)
+{
+ return -ENOTTY;
+}
#endif
#ifdef CONFIG_BLOCK
diff --git a/mm/filemap_xip.c b/mm/filemap_xip.c
index d808b72..38caad3 100644
--- a/mm/filemap_xip.c
+++ b/mm/filemap_xip.c
@@ -8,6 +8,7 @@
*
*/
+#include <linux/buffer_head.h>
#include <linux/fs.h>
#include <linux/pagemap.h>
#include <linux/export.h>
@@ -41,6 +42,103 @@ static struct page *xip_sparse_page(void)
return __xip_sparse_page;
}
+static ssize_t __xip_io(int rw, struct inode *inode, const struct iovec *iov,
+ loff_t offset, loff_t end, unsigned nr_segs,
+ get_block_t get_block, struct buffer_head *bh)
+{
+ ssize_t retval;
+ unsigned seg = 0;
+ unsigned len;
+ unsigned copied = 0;
+ loff_t max = offset;
+
+ while (offset < end) {
+ void __user *buf = iov[seg].iov_base + copied;
+ bool hole;
+
+ if (max == offset) {
+ sector_t block = offset >> inode->i_blkbits;
+ memset(bh, 0, sizeof(*bh));
+ bh->b_size = ALIGN(end - offset, PAGE_SIZE);
+ retval = get_block(inode, block, bh, 0);
+ if (retval)
+ break;
+ if (buffer_mapped(bh))
+ hole = false;
+ else
+ hole = true;
+ if (rw == WRITE && hole) {
+ bh->b_size = ALIGN(end - offset, PAGE_SIZE);
+ retval = get_block(inode, block, bh, 1);
+ if (retval)
+ break;
+ }
+ max = offset + bh->b_size;
+ }
+
+ len = min_t(unsigned, iov[seg].iov_len - copied, max - offset);
+
+ if (rw == WRITE)
+ len -= __copy_from_user_nocache(addr, buf, len);
+ else if (!hole)
+ len -= __copy_to_user(buf, addr, len);
+ else
+ len -= __clear_user(buf, len);
+
+ offset += len;
+ copied += len;
+ if (copied == iov[seg].iov_len) {
+ seg++;
+ copied = 0;
+ }
+ }
+
+ return retval;
+}
+
+/*
+ * Perform I/O to an XIP file. We follow the same rules as
+ * __blockdev_direct_IO with respect to locking
+ */
+ssize_t xip_io(int rw, struct kiocb *iocb, struct inode *inode,
+ const struct iovec *iov, loff_t offset, unsigned nr_segs,
+ get_block_t get_block, dio_iodone_t end_io, int flags)
+{
+ struct buffer_head bh;
+ unsigned seg;
+ ssize_t retval = -EINVAL;
+ loff_t end = offset;
+
+ for (seg = 0; seg < nr_segs; seg++)
+ end += iov[seg].iov_len;
+
+ 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, offset, end - 1);
+ if (retval) {
+ mutex_unlock(&inode->i_mutex);
+ goto out;
+ }
+ }
+
+ /* Protects against truncate */
+ atomic_inc(&inode->i_dio_count);
+
+ retval = __xip_io(rw, inode, iov, offset, end, nr_segs, get_block, &bh);
+
+ if ((flags & DIO_LOCKING) && (rw == READ))
+ mutex_unlock(&inode->i_mutex);
+
+ inode_dio_done(inode);
+
+ if (end_io)
+ end_io(iocb, offset, transferred, bh.b_private);
+ out:
+ return retval;
+}
+EXPORT_SYMBOL_GPL(xip_io);
+
/*
* 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
--
Matthew Wilcox Intel Open Source Technology Centre
"Bill, look, we understand that you're interested in selling us this
operating system, but compare it to ours. We can't possibly take such
a retrograde step."
--
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