squashfs: support reading fragments in readahead call

Add 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.

Link: https://lkml.kernel.org/r/20220617083810.337573-5-hsinyi@chromium.org
Signed-off-by: Phillip Lougher <phillip@squashfs.org.uk>
Signed-off-by: Hsin-Yi Wang <hsinyi@chromium.org>
Cc: Hou Tao <houtao1@huawei.com>
Cc: kernel test robot <lkp@intel.com>
Cc: Marek Szyprowski <m.szyprowski@samsung.com>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Miao Xie <miaoxie@huawei.com>
Cc: Xiongwei Song <Xiongwei.Song@windriver.com>
Cc: Zhang Yi <yi.zhang@huawei.com>
Cc: Zheng Liang <zhengliang6@huawei.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/fs/squashfs/file.c b/fs/squashfs/file.c
index 128ebe9..7ff0b03 100644 (file)
--- a/fs/squashfs/file.c
+++ b/fs/squashfs/file.c
@@ -496,6 +496,41 @@ out:
        return 0;
 }
 
+static 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;
@@ -512,9 +547,6 @@ static void squashfs_readahead(struct readahead_control *ractl)
 
        readahead_expand(ractl, start, (len | mask) + 1);
 
-       if (file_end == 0)
-               return;
-
        pages = kmalloc_array(max_pages, sizeof(void *), GFP_KERNEL);
        if (!pages)
                return;
@@ -540,6 +572,15 @@ static void squashfs_readahead(struct readahead_control *ractl)
                           (i_size_read(inode) & (msblk->block_size - 1)) :
                            msblk->block_size;
 
+               if (index == file_end && squashfs_i(inode)->fragment_block !=
+                                               SQUASHFS_INVALID_BLK) {
+                       res = squashfs_readahead_fragment(pages, nr_pages,
+                                                         expected);
+                       if (res)
+                               goto skip_pages;
+                       continue;
+               }
+
                bsize = read_blocklist(inode, index, &block);
                if (bsize == 0)
                        goto skip_pages;