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From:   Ritesh Harjani <ritesh.list@gmail.com>
To:     Theodore Ts'o <tytso@mit.edu>
Cc:     Harshad Shirwadkar <harshadshirwadkar@gmail.com>,
        Andreas Dilger <adilger@dilger.ca>,
        linux-ext4 <linux-ext4@vger.kernel.org>,
        Saranya Muruganandam <saranyamohan@google.com>,
        Ritesh Harjani <ritesh.list@gmail.com>
Subject: [RFC 12/13] libext2fs: dupfs: Add fs clone & merge api
Date:   Mon,  4 Jul 2022 12:37:01 +0530
Message-Id: <f1cbf256269cda5dfd489da677015b504a46341d.1656912918.git.ritesh.list@gmail.com>
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From: Saranya Muruganandam <saranyamohan@google.com>

This patch mainly adds "parent" & "clone_flags" member in ext2_filsys struct
for enabling multi-threading. Based on what CLONE flags will be passed from
the client of libext2fs down to ext2fs_clone_fs(), those structures/bitmaps will
be cloned (thread-aware child copy) and rest will be shared with the parent fs.

The same flags will also help to merge those cloned bitmap structures back into
the parent bitmaps when ext2fs_merge_fs() will be called with childfs struct.

Review couple of todos within the patch.
1. I think we don't need refcount here.
2. For io_channel_close(), I think that might be required here (even though
   earlier I thought it should be done by the caller), before freeing childfs.

Signed-off-by: Saranya Muruganandam <saranyamohan@google.com>
[added todos, modified naming, used #ifdef HAVE_PTHREAD, small bug fix in
calling io_channel_close(), later added a test case against this patch]
Signed-off-by: Ritesh Harjani <ritesh.list@gmail.com>
---
 lib/ext2fs/dupfs.c  | 149 ++++++++++++++++++++++++++++++++++++++++++++
 lib/ext2fs/ext2fs.h |  24 +++++++
 2 files changed, 173 insertions(+)

diff --git a/lib/ext2fs/dupfs.c b/lib/ext2fs/dupfs.c
index 02721e1a..8500a82c 100644
--- a/lib/ext2fs/dupfs.c
+++ b/lib/ext2fs/dupfs.c
@@ -14,8 +14,12 @@
 #if HAVE_UNISTD_H
 #include <unistd.h>
 #endif
+#if HAVE_PTHREAD_H
+#include <pthread.h>
+#endif
 #include <time.h>
 #include <string.h>
+#include <assert.h>

 #include "ext2_fs.h"
 #include "ext2fsP.h"
@@ -120,3 +124,148 @@ errout:

 }

+#ifdef HAVE_PTHREAD
+errcode_t ext2fs_clone_fs(ext2_filsys fs, ext2_filsys *dest, unsigned int flags)
+{
+	errcode_t retval;
+	ext2_filsys childfs;
+
+	EXT2_CHECK_MAGIC(fs, EXT2_ET_MAGIC_EXT2FS_FILSYS);
+
+	retval = ext2fs_get_mem(sizeof(struct struct_ext2_filsys), &childfs);
+	if (retval)
+		return retval;
+
+	/* make an exact copy implying lists and memory structures are shared */
+	memcpy(childfs, fs, sizeof(struct struct_ext2_filsys));
+	childfs->inode_map = NULL;
+	childfs->block_map = NULL;
+	childfs->badblocks = NULL;
+	childfs->dblist = NULL;
+
+	pthread_mutex_lock(&fs->refcount_mutex);
+	fs->refcount++;
+	pthread_mutex_unlock(&fs->refcount_mutex);
+
+	if ((flags & EXT2FS_CLONE_INODE) && fs->inode_map) {
+		retval = ext2fs_copy_bitmap(fs->inode_map, &childfs->inode_map);
+		if (retval)
+			return retval;
+		childfs->inode_map->fs = childfs;
+	}
+
+	if ((flags & EXT2FS_CLONE_BLOCK) && fs->block_map) {
+		retval = ext2fs_copy_bitmap(fs->block_map, &childfs->block_map);
+		if (retval)
+			return retval;
+		childfs->block_map->fs = childfs;
+	}
+
+	if ((flags & EXT2FS_CLONE_BADBLOCKS) && fs->badblocks) {
+		retval = ext2fs_badblocks_copy(fs->badblocks, &childfs->badblocks);
+		if (retval)
+			return retval;
+	}
+
+	if ((flags & EXT2FS_CLONE_DBLIST) && fs->dblist) {
+		retval = ext2fs_copy_dblist(fs->dblist, &childfs->dblist);
+		if (retval)
+			return retval;
+		childfs->dblist->fs = childfs;
+	}
+
+	/* icache when NULL will be rebuilt if needed */
+	childfs->icache = NULL;
+
+	childfs->clone_flags = flags;
+	childfs->parent = fs;
+	*dest = childfs;
+
+	return 0;
+}
+
+errcode_t ext2fs_merge_fs(ext2_filsys fs)
+{
+	errcode_t retval = 0;
+	ext2_filsys dest = fs->parent;
+	ext2_filsys src = fs;
+	unsigned int flags = fs->clone_flags;
+
+	pthread_mutex_lock(&fs->refcount_mutex);
+	fs->refcount--;
+	assert(fs->refcount >= 0);
+	pthread_mutex_unlock(&fs->refcount_mutex);
+
+	if ((flags & EXT2FS_CLONE_INODE) && src->inode_map) {
+		if (dest->inode_map == NULL) {
+			dest->inode_map = src->inode_map;
+			src->inode_map = NULL;
+		} else {
+			retval = ext2fs_merge_bitmap(src->inode_map, dest->inode_map, NULL, NULL);
+			if (retval)
+				goto out;
+		}
+		dest->inode_map->fs = dest;
+	}
+
+	if ((flags & EXT2FS_CLONE_BLOCK) && src->block_map) {
+		if (dest->block_map == NULL) {
+			dest->block_map = src->block_map;
+			src->block_map = NULL;
+		} else {
+			retval = ext2fs_merge_bitmap(src->block_map, dest->block_map, NULL, NULL);
+			if (retval)
+				goto out;
+		}
+		dest->block_map->fs = dest;
+	}
+
+	if ((flags & EXT2FS_CLONE_BADBLOCKS) && src->badblocks) {
+		if (dest->badblocks == NULL)
+			retval = ext2fs_badblocks_copy(src->badblocks, &dest->badblocks);
+		else
+			retval = ext2fs_badblocks_merge(src->badblocks, dest->badblocks);
+		if (retval)
+			goto out;
+	}
+
+	if ((flags & EXT2FS_CLONE_DBLIST) && src->dblist) {
+		if (dest->dblist == NULL) {
+			dest->dblist = src->dblist;
+			src->dblist = NULL;
+		} else {
+			retval = ext2fs_merge_dblist(src->dblist, dest->dblist);
+			if (retval)
+				goto out;
+		}
+		dest->dblist->fs = dest;
+	}
+
+	dest->flags |= src->flags;
+	if (!(dest->flags & EXT2_FLAG_VALID))
+		ext2fs_unmark_valid(dest);
+
+	if (src->icache) {
+		ext2fs_free_inode_cache(src->icache);
+		src->icache = NULL;
+	}
+
+out:
+	/* TODO check if io_channel_close is called correctly here? */
+	if (src->io)
+		io_channel_close(src->io);
+
+	if ((flags & EXT2FS_CLONE_INODE) && src->inode_map)
+		ext2fs_free_generic_bmap(src->inode_map);
+	if ((flags & EXT2FS_CLONE_BLOCK) && src->block_map)
+		ext2fs_free_generic_bmap(src->block_map);
+	if ((flags & EXT2FS_CLONE_BADBLOCKS) && src->badblocks)
+		ext2fs_badblocks_list_free(src->badblocks);
+	if ((flags & EXT2FS_CLONE_DBLIST) && src->dblist)
+		ext2fs_free_dblist(src->dblist);
+
+	ext2fs_free_mem(&src);
+
+	return retval;
+}
+#endif
diff --git a/lib/ext2fs/ext2fs.h b/lib/ext2fs/ext2fs.h
index 29e7be9f..6daa7832 100644
--- a/lib/ext2fs/ext2fs.h
+++ b/lib/ext2fs/ext2fs.h
@@ -12,6 +12,10 @@
 #ifndef _EXT2FS_EXT2FS_H
 #define _EXT2FS_EXT2FS_H

+#ifdef HAVE_PTHREAD_H
+#include <pthread.h>
+#endif
+
 #ifdef __GNUC__
 #define EXT2FS_ATTR(x) __attribute__(x)
 #else
@@ -330,6 +334,14 @@ struct struct_ext2_filsys {
 	struct ext2fs_hashmap* block_sha_map;

 	const struct ext2fs_nls_table *encoding;
+
+#ifdef HAVE_PTHREAD
+	struct struct_ext2_filsys *parent;
+	/* TODO do we need refcount? */
+	size_t refcount;
+	pthread_mutex_t refcount_mutex;
+	unsigned int clone_flags;
+#endif
 };

 #if EXT2_FLAT_INCLUDES
@@ -1056,6 +1068,18 @@ extern errcode_t ext2fs_move_blocks(ext2_filsys fs,
 /* check_desc.c */
 extern errcode_t ext2fs_check_desc(ext2_filsys fs);

+#ifdef HAVE_PTHREAD
+/* flags for ext2fs_clone_fs */
+#define EXT2FS_CLONE_BLOCK 			0x0001
+#define EXT2FS_CLONE_INODE 			0x0002
+#define EXT2FS_CLONE_BADBLOCKS 		0x0004
+#define EXT2FS_CLONE_DBLIST			0x0008
+
+extern errcode_t ext2fs_clone_fs(ext2_filsys fs, ext2_filsys *dest,
+								 unsigned int flags);
+extern errcode_t ext2fs_merge_fs(ext2_filsys fs);
+#endif
+
 /* closefs.c */
 extern errcode_t ext2fs_close(ext2_filsys fs);
 extern errcode_t ext2fs_close2(ext2_filsys fs, int flags);
--
2.35.3