Re: [PATCH v6] iomap: support tail packing inline read

Christoph Hellwig
2021-07-22T05:39:53Z

I think some of the language here is confusing - mostly about tail
packing when we otherwise use inline data. Can you take a look at
the version below? This mostly cleans up the terminology, adds a
new helper to check the size, and removes the error on trying to
write with a non-zero pos, as it can be trivially supported now.

---
From 0f9c6ac6c2e372739b29195d25bebb8dd87e583a Mon Sep 17 00:00:00 2001
From: Gao Xiang <hsiangkao@linux.alibaba.com>
Date: Thu, 22 Jul 2021 11:17:29 +0800
Subject: iomap: make inline data support more flexible

Add support for offsets into the inline data page at iomap->inline_data
to cater for the EROFS tailpackng case where a small data is stored
right after the inode.

Signed-off-by: Gao Xiang <hsiangkao@linux.alibaba.com>
---
fs/iomap/buffered-io.c | 35 ++++++++++++++++++-----------------
fs/iomap/direct-io.c | 10 ++++++----
include/linux/iomap.h | 14 ++++++++++++++
3 files changed, 38 insertions(+), 21 deletions(-)

diff --git a/fs/iomap/buffered-io.c b/fs/iomap/buffered-io.c
index 87ccb3438becd9..0597f5c186a33f 100644
--- a/fs/iomap/buffered-io.c
+++ b/fs/iomap/buffered-io.c
@@ -205,25 +205,29 @@ struct iomap_readpage_ctx {
struct readahead_control *rac;
};

-static void
-iomap_read_inline_data(struct inode *inode, struct page *page,
- struct iomap *iomap)
+static int iomap_read_inline_data(struct inode *inode, struct page *page,
+ struct iomap *iomap, loff_t pos)
{
- size_t size = i_size_read(inode);
+ size_t size = iomap->length + iomap->offset - pos;
void *addr;

if (PageUptodate(page))
- return;
+ return PAGE_SIZE;

- BUG_ON(page_has_private(page));
- BUG_ON(page->index);
- BUG_ON(size > PAGE_SIZE - offset_in_page(iomap->inline_data));
+ /* inline data must start page aligned in the file */
+ if (WARN_ON_ONCE(offset_in_page(pos)))
+ return -EIO;
+ if (WARN_ON_ONCE(!iomap_inline_data_size_valid(iomap)))
+ return -EIO;
+ if (WARN_ON_ONCE(page_has_private(page)))
+ return -EIO;

addr = kmap_atomic(page);
- memcpy(addr, iomap->inline_data, size);
+ memcpy(addr, iomap_inline_buf(iomap, pos), size);
memset(addr + size, 0, PAGE_SIZE - size);
kunmap_atomic(addr);
SetPageUptodate(page);
+ return PAGE_SIZE;
}

static inline bool iomap_block_needs_zeroing(struct inode *inode,
@@ -246,11 +250,8 @@ iomap_readpage_actor(struct inode *inode, loff_t pos, loff_t length, void *data,
unsigned poff, plen;
sector_t sector;

- if (iomap->type == IOMAP_INLINE) {
- WARN_ON_ONCE(pos);
- iomap_read_inline_data(inode, page, iomap);
- return PAGE_SIZE;
- }
+ if (iomap->type == IOMAP_INLINE)
+ return iomap_read_inline_data(inode, page, iomap, pos);

/* zero post-eof blocks as the page may be mapped */
iop = iomap_page_create(inode, page);
@@ -618,14 +619,14 @@ iomap_write_begin(struct inode *inode, loff_t pos, unsigned len, unsigned flags,
}

if (srcmap->type == IOMAP_INLINE)
- iomap_read_inline_data(inode, page, srcmap);
+ status = iomap_read_inline_data(inode, page, srcmap, pos);
else if (iomap->flags & IOMAP_F_BUFFER_HEAD)
status = __block_write_begin_int(page, pos, len, NULL, srcmap);
else
status = __iomap_write_begin(inode, pos, len, flags, page,
srcmap);

- if (unlikely(status))
+ if (unlikely(status < 0))
goto out_unlock;

*pagep = page;
@@ -675,7 +676,7 @@ static size_t iomap_write_end_inline(struct inode *inode, struct page *page,

flush_dcache_page(page);
addr = kmap_atomic(page);
- memcpy(iomap->inline_data + pos, addr + pos, copied);
+ memcpy(iomap_inline_buf(iomap, pos), addr + pos, copied);
kunmap_atomic(addr);

mark_inode_dirty(inode);
diff --git a/fs/iomap/direct-io.c b/fs/iomap/direct-io.c
index 9398b8c31323b3..a6aaea2764a55f 100644
--- a/fs/iomap/direct-io.c
+++ b/fs/iomap/direct-io.c
@@ -378,23 +378,25 @@ iomap_dio_inline_actor(struct inode *inode, loff_t pos, loff_t length,
struct iomap_dio *dio, struct iomap *iomap)
{
struct iov_iter *iter = dio->submit.iter;
+ void *dst = iomap_inline_buf(iomap, pos);
size_t copied;

- BUG_ON(pos + length > PAGE_SIZE - offset_in_page(iomap->inline_data));
+ if (WARN_ON_ONCE(!iomap_inline_data_size_valid(iomap)))
+ return -EIO;

if (dio->flags & IOMAP_DIO_WRITE) {
loff_t size = inode->i_size;

if (pos > size)
- memset(iomap->inline_data + size, 0, pos - size);
- copied = copy_from_iter(iomap->inline_data + pos, length, iter);
+ memset(iomap_inline_buf(iomap, size), 0, pos - size);
+ copied = copy_from_iter(dst, length, iter);
if (copied) {
if (pos + copied > size)
i_size_write(inode, pos + copied);
mark_inode_dirty(inode);
}
} else {
- copied = copy_to_iter(iomap->inline_data + pos, length, iter);
+ copied = copy_to_iter(dst, length, iter);
}
dio->size += copied;
return copied;
diff --git a/include/linux/iomap.h b/include/linux/iomap.h
index 479c1da3e2211e..5efae7153912ed 100644
--- a/include/linux/iomap.h
+++ b/include/linux/iomap.h
@@ -97,6 +97,20 @@ iomap_sector(struct iomap *iomap, loff_t pos)
return (iomap->addr + pos - iomap->offset) >> SECTOR_SHIFT;
}

+static inline void *iomap_inline_buf(const struct iomap *iomap, loff_t pos)
+{
+ return iomap->inline_data - iomap->offset + pos;
+}
+
+/*
+ * iomap->inline_data is a potentially kmapped page, ensure it never crosseѕ a
+ * page boundary.
+ */
+static inline bool iomap_inline_data_size_valid(const struct iomap *iomap)
+{
+ return iomap->length <= PAGE_SIZE - offset_in_page(iomap->inline_data);
+}
+
/*
* When a filesystem sets page_ops in an iomap mapping it returns, page_prepare
* and page_done will be called for each page written to. This only applies to
--
2.30.2