[PATCH 2/3] mm: Add folio_fill_tail() and use it in iomap

Matthew Wilcox (Oracle)
2023-11-07T21:27:00Z

The iomap code was limited to PAGE_SIZE bytes; generalise it to cover
an arbitrary-sized folio, and move it to be a common helper.

Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
---
fs/iomap/buffered-io.c | 14 ++------------
include/linux/highmem.h | 38 ++++++++++++++++++++++++++++++++++++++
2 files changed, 40 insertions(+), 12 deletions(-)

diff --git a/fs/iomap/buffered-io.c b/fs/iomap/buffered-io.c
index f72df2babe56..093c4515b22a 100644
--- a/fs/iomap/buffered-io.c
+++ b/fs/iomap/buffered-io.c
@@ -305,28 +305,18 @@ static int iomap_read_inline_data(const struct iomap_iter *iter,
{
const struct iomap *iomap = iomap_iter_srcmap(iter);
size_t size = i_size_read(iter->inode) - iomap->offset;
- size_t poff = offset_in_page(iomap->offset);
size_t offset = offset_in_folio(folio, iomap->offset);
- void *addr;

if (folio_test_uptodate(folio))
return 0;

- if (WARN_ON_ONCE(size > PAGE_SIZE - poff))
- return -EIO;
- if (WARN_ON_ONCE(size > PAGE_SIZE -
- offset_in_page(iomap->inline_data)))
- return -EIO;
if (WARN_ON_ONCE(size > iomap->length))
return -EIO;
if (offset > 0)
ifs_alloc(iter->inode, folio, iter->flags);

- addr = kmap_local_folio(folio, offset);
- memcpy(addr, iomap->inline_data, size);
- memset(addr + size, 0, PAGE_SIZE - poff - size);
- kunmap_local(addr);
- iomap_set_range_uptodate(folio, offset, PAGE_SIZE - poff);
+ folio_fill_tail(folio, offset, iomap->inline_data, size);
+ iomap_set_range_uptodate(folio, offset, folio_size(folio) - offset);
return 0;
}

diff --git a/include/linux/highmem.h b/include/linux/highmem.h
index 1b81416196dd..0fbb60ffefc9 100644
--- a/include/linux/highmem.h
+++ b/include/linux/highmem.h
@@ -521,6 +521,44 @@ static inline __must_check void *folio_zero_tail(struct folio *folio,
return kaddr;
}

+/**
+ * folio_fill_tail - Copy some data to a folio and pad with zeroes.
+ * @folio: The destination folio.
+ * @offset: The offset into @folio at which to start copying.
+ * @from: The data to copy.
+ * @len: How many bytes of data to copy.
+ *
+ * This function is most useful for filesystems which support inline data.
+ * When they want to copy data from the inode into the page cache, this
+ * function does everything for them. It supports large folios even on
+ * HIGHMEM configurations.
+ */
+static inline void folio_fill_tail(struct folio *folio, size_t offset,
+ const char *from, size_t len)
+{
+ char *to = kmap_local_folio(folio, offset);
+
+ VM_BUG_ON(offset + len > folio_size(folio));
+
+ if (folio_test_highmem(folio)) {
+ size_t max = PAGE_SIZE - offset_in_page(offset);
+
+ while (len > max) {
+ memcpy(to, from, max);
+ kunmap_local(to);
+ len -= max;
+ from += max;
+ offset += max;
+ max = PAGE_SIZE;
+ to = kmap_local_folio(folio, offset);
+ }
+ }
+
+ memcpy(to, from, len);
+ to = folio_zero_tail(folio, offset, to);
+ kunmap_local(to);
+}
+
/**
* memcpy_from_file_folio - Copy some bytes from a file folio.
* @to: The destination buffer.
--
2.42.0