[PATCH 4/3] squashfs: support reading fragments in readahead call

[Phillip Lougher]

This patch adds a function which can be used to read fragments in the
readahead call.

This function is necessary because filesystems built with the -tailends
(or -always-use-fragments) option may have fragments present which
cannot be currently handled.

Signed-off-by: Phillip Lougher <phillip@xxxxxxxxxxxxxxx>
---
 fs/squashfs/file.c | 35 +++++++++++++++++++++++++++++++++++
 1 file changed, 35 insertions(+)

diff --git a/fs/squashfs/file.c b/fs/squashfs/file.c
index f0c64ee272d5..3a4cce16d7da 100644
--- a/fs/squashfs/file.c
+++ b/fs/squashfs/file.c
@@ -497,6 +497,41 @@ static int squashfs_read_folio(struct file *file, struct folio *folio)
 	return res;
 }
 
+static unsigned int squashfs_readahead_fragment(struct page **page,
+	unsigned int pages, unsigned int expected)
+{
+	struct inode *inode = page[0]->mapping->host;
+	struct squashfs_cache_entry *buffer = squashfs_get_fragment(inode->i_sb,
+		squashfs_i(inode)->fragment_block,
+		squashfs_i(inode)->fragment_size);
+	struct squashfs_sb_info *msblk = inode->i_sb->s_fs_info;
+	unsigned int n, mask = (1 << (msblk->block_log - PAGE_SHIFT)) - 1;
+
+	if (buffer->error)
+		goto out;
+
+	expected += squashfs_i(inode)->fragment_offset;
+
+	for (n = 0; n < pages; n++) {
+		unsigned int base = (page[n]->index & mask) << PAGE_SHIFT;
+		unsigned int offset = base + squashfs_i(inode)->fragment_offset;
+
+		if (expected > offset) {
+			unsigned int avail = min_t(unsigned int, expected -
+				offset, PAGE_SIZE);
+
+			squashfs_fill_page(page[n], buffer, offset, avail);
+		}
+
+		unlock_page(page[n]);
+		put_page(page[n]);
+	}
+
+out:
+	squashfs_cache_put(buffer);
+	return buffer->error;
+}
+
 static void squashfs_readahead(struct readahead_control *ractl)
 {
 	struct inode *inode = ractl->mapping->host;
-- 
2.34.1