iomap: move the SEEK_HOLE code into a separate file

Move the SEEK_HOLE/SEEK_DATA code into a separate file so that we can
group related functions in a single file instead of having a single
enormous source file.

Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>

2 files changed, 216 insertions, 1 deletions

diff --git a/fs/iomap/Makefile b/fs/iomap/Makefile
index 44cef914020f..5dfe8b5cf330 100644
--- a/fs/iomap/Makefile
+++ b/fs/iomap/Makefile
@@ -6,6 +6,7 @@
 obj-$(CONFIG_FS_IOMAP)		+= iomap.o
 
 iomap-y				+= \
-					fiemap.o
+					fiemap.o \
+					seek.o
 
 iomap-$(CONFIG_SWAP)		+= swapfile.o
diff --git a/fs/iomap/seek.c b/fs/iomap/seek.c
new file mode 100644
index 000000000000..715442eb71aa
--- /dev/null
+++ b/fs/iomap/seek.c
@@ -0,0 +1,214 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright (C) 2017 Red Hat, Inc.
+ * Copyright (c) 2018 Christoph Hellwig.
+ */
+#include <linux/module.h>
+#include <linux/compiler.h>
+#include <linux/fs.h>
+#include <linux/iomap.h>
+#include <linux/pagemap.h>
+#include <linux/pagevec.h>
+
+#include "../internal.h"
+
+/*
+ * Seek for SEEK_DATA / SEEK_HOLE within @page, starting at @lastoff.
+ * Returns true if found and updates @lastoff to the offset in file.
+ */
+static bool
+page_seek_hole_data(struct inode *inode, struct page *page, loff_t *lastoff,
+		int whence)
+{
+	const struct address_space_operations *ops = inode->i_mapping->a_ops;
+	unsigned int bsize = i_blocksize(inode), off;
+	bool seek_data = whence == SEEK_DATA;
+	loff_t poff = page_offset(page);
+
+	if (WARN_ON_ONCE(*lastoff >= poff + PAGE_SIZE))
+		return false;
+
+	if (*lastoff < poff) {
+		/*
+		 * Last offset smaller than the start of the page means we found
+		 * a hole:
+		 */
+		if (whence == SEEK_HOLE)
+			return true;
+		*lastoff = poff;
+	}
+
+	/*
+	 * Just check the page unless we can and should check block ranges:
+	 */
+	if (bsize == PAGE_SIZE || !ops->is_partially_uptodate)
+		return PageUptodate(page) == seek_data;
+
+	lock_page(page);
+	if (unlikely(page->mapping != inode->i_mapping))
+		goto out_unlock_not_found;
+
+	for (off = 0; off < PAGE_SIZE; off += bsize) {
+		if (offset_in_page(*lastoff) >= off + bsize)
+			continue;
+		if (ops->is_partially_uptodate(page, off, bsize) == seek_data) {
+			unlock_page(page);
+			return true;
+		}
+		*lastoff = poff + off + bsize;
+	}
+
+out_unlock_not_found:
+	unlock_page(page);
+	return false;
+}
+
+/*
+ * Seek for SEEK_DATA / SEEK_HOLE in the page cache.
+ *
+ * Within unwritten extents, the page cache determines which parts are holes
+ * and which are data: uptodate buffer heads count as data; everything else
+ * counts as a hole.
+ *
+ * Returns the resulting offset on successs, and -ENOENT otherwise.
+ */
+static loff_t
+page_cache_seek_hole_data(struct inode *inode, loff_t offset, loff_t length,
+		int whence)
+{
+	pgoff_t index = offset >> PAGE_SHIFT;
+	pgoff_t end = DIV_ROUND_UP(offset + length, PAGE_SIZE);
+	loff_t lastoff = offset;
+	struct pagevec pvec;
+
+	if (length <= 0)
+		return -ENOENT;
+
+	pagevec_init(&pvec);
+
+	do {
+		unsigned nr_pages, i;
+
+		nr_pages = pagevec_lookup_range(&pvec, inode->i_mapping, &index,
+						end - 1);
+		if (nr_pages == 0)
+			break;
+
+		for (i = 0; i < nr_pages; i++) {
+			struct page *page = pvec.pages[i];
+
+			if (page_seek_hole_data(inode, page, &lastoff, whence))
+				goto check_range;
+			lastoff = page_offset(page) + PAGE_SIZE;
+		}
+		pagevec_release(&pvec);
+	} while (index < end);
+
+	/* When no page at lastoff and we are not done, we found a hole. */
+	if (whence != SEEK_HOLE)
+		goto not_found;
+
+check_range:
+	if (lastoff < offset + length)
+		goto out;
+not_found:
+	lastoff = -ENOENT;
+out:
+	pagevec_release(&pvec);
+	return lastoff;
+}
+
+
+static loff_t
+iomap_seek_hole_actor(struct inode *inode, loff_t offset, loff_t length,
+		      void *data, struct iomap *iomap)
+{
+	switch (iomap->type) {
+	case IOMAP_UNWRITTEN:
+		offset = page_cache_seek_hole_data(inode, offset, length,
+						   SEEK_HOLE);
+		if (offset < 0)
+			return length;
+		/* fall through */
+	case IOMAP_HOLE:
+		*(loff_t *)data = offset;
+		return 0;
+	default:
+		return length;
+	}
+}
+
+loff_t
+iomap_seek_hole(struct inode *inode, loff_t offset, const struct iomap_ops *ops)
+{
+	loff_t size = i_size_read(inode);
+	loff_t length = size - offset;
+	loff_t ret;
+
+	/* Nothing to be found before or beyond the end of the file. */
+	if (offset < 0 || offset >= size)
+		return -ENXIO;
+
+	while (length > 0) {
+		ret = iomap_apply(inode, offset, length, IOMAP_REPORT, ops,
+				  &offset, iomap_seek_hole_actor);
+		if (ret < 0)
+			return ret;
+		if (ret == 0)
+			break;
+
+		offset += ret;
+		length -= ret;
+	}
+
+	return offset;
+}
+EXPORT_SYMBOL_GPL(iomap_seek_hole);
+
+static loff_t
+iomap_seek_data_actor(struct inode *inode, loff_t offset, loff_t length,
+		      void *data, struct iomap *iomap)
+{
+	switch (iomap->type) {
+	case IOMAP_HOLE:
+		return length;
+	case IOMAP_UNWRITTEN:
+		offset = page_cache_seek_hole_data(inode, offset, length,
+						   SEEK_DATA);
+		if (offset < 0)
+			return length;
+		/*FALLTHRU*/
+	default:
+		*(loff_t *)data = offset;
+		return 0;
+	}
+}
+
+loff_t
+iomap_seek_data(struct inode *inode, loff_t offset, const struct iomap_ops *ops)
+{
+	loff_t size = i_size_read(inode);
+	loff_t length = size - offset;
+	loff_t ret;
+
+	/* Nothing to be found before or beyond the end of the file. */
+	if (offset < 0 || offset >= size)
+		return -ENXIO;
+
+	while (length > 0) {
+		ret = iomap_apply(inode, offset, length, IOMAP_REPORT, ops,
+				  &offset, iomap_seek_data_actor);
+		if (ret < 0)
+			return ret;
+		if (ret == 0)
+			break;
+
+		offset += ret;
+		length -= ret;
+	}
+
+	if (length <= 0)
+		return -ENXIO;
+	return offset;
+}
+EXPORT_SYMBOL_GPL(iomap_seek_data);