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Message-Id: <20250923220652.568416-3-phillip@squashfs.org.uk>
Date: Tue, 23 Sep 2025 23:06:52 +0100
From: Phillip Lougher <phillip@...ashfs.org.uk>
To: akpm@...ux-foundation.org,
linux-kernel@...r.kernel.org
Cc: Phillip Lougher <phillip@...ashfs.org.uk>
Subject: [PATCH 2/2] Squashfs: add SEEK_DATA/SEEK_HOLE support
Add support for SEEK_DATA and SEEK_HOLE lseek() whence values.
These allow much faster searches for holes and data in sparse files,
which can significantly speed up file copying, e.g.
before (GNU coreutils, Debian 13):
cp --sparse=always big-file /
took real 11m58s, user 0m5.764s, sys 11m48s
after:
real 0.047s, user 0.000s, sys 0.027s
Where big-file has a 256 GB hole followed by 47 KB of data.
Signed-off-by: Phillip Lougher <phillip@...ashfs.org.uk>
---
fs/squashfs/file.c | 137 +++++++++++++++++++++++++++++++++++---
fs/squashfs/inode.c | 4 +-
fs/squashfs/squashfs.h | 1 +
fs/squashfs/squashfs_fs.h | 1 +
4 files changed, 130 insertions(+), 13 deletions(-)
diff --git a/fs/squashfs/file.c b/fs/squashfs/file.c
index ce7d661d5ad8..1582e0637a7e 100644
--- a/fs/squashfs/file.c
+++ b/fs/squashfs/file.c
@@ -307,7 +307,8 @@ static int fill_meta_index(struct inode *inode, int index,
all_done:
*index_block = cur_index_block;
*index_offset = cur_offset;
- *data_block = cur_data_block;
+ if (data_block)
+ *data_block = cur_data_block;
/*
* Scale cache index (cache slot entry) to index
@@ -324,17 +325,15 @@ static int fill_meta_index(struct inode *inode, int index,
* Get the on-disk location and compressed size of the datablock
* specified by index. Fill_meta_index() does most of the work.
*/
-static int read_blocklist(struct inode *inode, int index, u64 *block)
+static int read_blocklist_ptrs(struct inode *inode, int index, u64 *start,
+ int *offset, u64 *block)
{
- u64 start;
long long blks;
- int offset;
__le32 size;
- int res = fill_meta_index(inode, index, &start, &offset, block);
+ int res = fill_meta_index(inode, index, start, offset, block);
- TRACE("read_blocklist: res %d, index %d, start 0x%llx, offset"
- " 0x%x, block 0x%llx\n", res, index, start, offset,
- *block);
+ TRACE("read_blocklist: res %d, index %d, start 0x%llx, offset 0x%x, block 0x%llx\n",
+ res, index, *start, *offset, block ? *block : 0);
if (res < 0)
return res;
@@ -346,22 +345,31 @@ static int read_blocklist(struct inode *inode, int index, u64 *block)
* extra block indexes needed.
*/
if (res < index) {
- blks = read_indexes(inode->i_sb, index - res, &start, &offset);
+ blks = read_indexes(inode->i_sb, index - res, start, offset);
if (blks < 0)
return (int) blks;
- *block += blks;
+ if (block)
+ *block += blks;
}
/*
* Read length of block specified by index.
*/
- res = squashfs_read_metadata(inode->i_sb, &size, &start, &offset,
+ res = squashfs_read_metadata(inode->i_sb, &size, start, offset,
sizeof(size));
if (res < 0)
return res;
return squashfs_block_size(size);
}
+static inline int read_blocklist(struct inode *inode, int index, u64 *block)
+{
+ u64 start;
+ int offset;
+
+ return read_blocklist_ptrs(inode, index, &start, &offset, block);
+}
+
static bool squashfs_fill_page(struct folio *folio,
struct squashfs_cache_entry *buffer, size_t offset,
size_t avail)
@@ -658,7 +666,114 @@ static void squashfs_readahead(struct readahead_control *ractl)
kfree(pages);
}
+static loff_t seek_hole_data(struct file *file, loff_t offset, int whence)
+{
+ struct inode *inode = file->f_mapping->host;
+ struct super_block *sb = inode->i_sb;
+ struct squashfs_sb_info *msblk = sb->s_fs_info;
+ u64 start, index = offset >> msblk->block_log;
+ u64 file_end = (i_size_read(inode) + msblk->block_size - 1) >> msblk->block_log;
+ int s_offset, length;
+ __le32 *blist = NULL;
+
+ /* reject offset if negative or beyond file end */
+ if ((unsigned long long)offset >= i_size_read(inode))
+ return -ENXIO;
+
+ /* is offset within tailend and is tailend packed into a fragment? */
+ if (index + 1 == file_end &&
+ squashfs_i(inode)->fragment_block != SQUASHFS_INVALID_BLK) {
+ if (whence == SEEK_DATA)
+ return offset;
+
+ /* there is an implicit hole at the end of any file */
+ return i_size_read(inode);
+ }
+
+ length = read_blocklist_ptrs(inode, index, &start, &s_offset, NULL);
+ if (length < 0)
+ return length;
+
+ /* nothing more to do if offset matches desired whence value */
+ if ((length == 0 && whence == SEEK_HOLE) ||
+ (length && whence == SEEK_DATA))
+ return offset;
+
+ /* skip scanning forwards if we're at file end */
+ if (++ index == file_end)
+ goto not_found;
+
+ blist = kmalloc(SQUASHFS_SCAN_INDEXES << 2, GFP_KERNEL);
+ if (blist == NULL) {
+ ERROR("%s: Failed to allocate block_list\n", __func__);
+ return -ENOMEM;
+ }
+
+ while (index < file_end) {
+ int i, indexes = min(file_end - index, SQUASHFS_SCAN_INDEXES);
+
+ offset = squashfs_read_metadata(sb, blist, &start, &s_offset, indexes << 2);
+ if (offset < 0)
+ goto finished;
+
+ for (i = 0; i < indexes; i++) {
+ length = squashfs_block_size(blist[i]);
+ if (length < 0) {
+ offset = length;
+ goto finished;
+ }
+
+ /* does this block match desired whence value? */
+ if ((length == 0 && whence == SEEK_HOLE) ||
+ (length && whence == SEEK_DATA)) {
+ offset = (index + i) << msblk->block_log;
+ goto finished;
+ }
+ }
+
+ index += indexes;
+ }
+
+not_found:
+ /* whence value determines what happens */
+ if (whence == SEEK_DATA)
+ offset = -ENXIO;
+ else
+ /* there is an implicit hole at the end of any file */
+ offset = i_size_read(inode);
+
+finished:
+ kfree(blist);
+ return offset;
+}
+
+static loff_t squashfs_llseek(struct file *file, loff_t offset, int whence)
+{
+ struct inode *inode = file->f_mapping->host;
+
+ switch (whence) {
+ default:
+ return generic_file_llseek(file, offset, whence);
+ case SEEK_DATA:
+ case SEEK_HOLE:
+ offset = seek_hole_data(file, offset, whence);
+ break;
+ }
+
+ if (offset < 0)
+ return offset;
+
+ return vfs_setpos(file, offset, inode->i_sb->s_maxbytes);
+}
+
const struct address_space_operations squashfs_aops = {
.read_folio = squashfs_read_folio,
.readahead = squashfs_readahead
};
+
+const struct file_operations squashfs_file_operations = {
+ .llseek = squashfs_llseek,
+ .read_iter = generic_file_read_iter,
+ .mmap_prepare = generic_file_readonly_mmap_prepare,
+ .splice_read = filemap_splice_read
+};
diff --git a/fs/squashfs/inode.c b/fs/squashfs/inode.c
index 77eec1772998..5920a33e44a1 100644
--- a/fs/squashfs/inode.c
+++ b/fs/squashfs/inode.c
@@ -164,7 +164,7 @@ int squashfs_read_inode(struct inode *inode, long long ino)
}
set_nlink(inode, 1);
- inode->i_fop = &generic_ro_fops;
+ inode->i_fop = &squashfs_file_operations;
inode->i_mode |= S_IFREG;
inode->i_blocks = ((inode->i_size - 1) >> 9) + 1;
squashfs_i(inode)->fragment_block = frag_blk;
@@ -217,7 +217,7 @@ int squashfs_read_inode(struct inode *inode, long long ino)
xattr_id = le32_to_cpu(sqsh_ino->xattr);
set_nlink(inode, le32_to_cpu(sqsh_ino->nlink));
inode->i_op = &squashfs_inode_ops;
- inode->i_fop = &generic_ro_fops;
+ inode->i_fop = &squashfs_file_operations;
inode->i_mode |= S_IFREG;
inode->i_blocks = (inode->i_size -
le64_to_cpu(sqsh_ino->sparse) + 511) >> 9;
diff --git a/fs/squashfs/squashfs.h b/fs/squashfs/squashfs.h
index 218868b20f16..4851bd964502 100644
--- a/fs/squashfs/squashfs.h
+++ b/fs/squashfs/squashfs.h
@@ -107,6 +107,7 @@ extern const struct address_space_operations squashfs_aops;
/* inode.c */
extern const struct inode_operations squashfs_inode_ops;
+extern const struct file_operations squashfs_file_operations;
/* namei.c */
extern const struct inode_operations squashfs_dir_inode_ops;
diff --git a/fs/squashfs/squashfs_fs.h b/fs/squashfs/squashfs_fs.h
index 95f8e8901768..a955d9369749 100644
--- a/fs/squashfs/squashfs_fs.h
+++ b/fs/squashfs/squashfs_fs.h
@@ -208,6 +208,7 @@ static inline int squashfs_block_size(__le32 raw)
#define SQUASHFS_META_INDEXES (SQUASHFS_METADATA_SIZE / sizeof(unsigned int))
#define SQUASHFS_META_ENTRIES 127
#define SQUASHFS_META_SLOTS 8
+#define SQUASHFS_SCAN_INDEXES 1024
struct meta_entry {
u64 data_block;
--
2.39.5
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