diff --git a/contrib/android/Android.bp b/contrib/android/Android.bp
index f7fbf66..67844f9 100644
--- a/contrib/android/Android.bp
+++ b/contrib/android/Android.bp
@@ -16,7 +16,6 @@
         "base_fs.c",
         "perms.c",
         "basefs_allocator.c",
-        "hashmap.c",
     ],
     target: {
         host: {
diff --git a/contrib/android/Android.mk b/contrib/android/Android.mk
index bdfdece..68d925d 100644
--- a/contrib/android/Android.mk
+++ b/contrib/android/Android.mk
@@ -10,7 +10,6 @@
         base_fs.c \
         perms.c \
         basefs_allocator.c \
-        hashmap.c \
 
 e2fsdroid_cflags := -W -Wall -Werror -Wno-error=macro-redefined
 
diff --git a/contrib/android/base_fs.c b/contrib/android/base_fs.c
index 2dcb5fe..1420305 100644
--- a/contrib/android/base_fs.c
+++ b/contrib/android/base_fs.c
@@ -99,24 +99,25 @@
 	}
 }
 
-struct hashmap *basefs_parse(const char *file, const char *mountpoint)
+struct ext2fs_hashmap *basefs_parse(const char *file, const char *mountpoint)
 {
 	int err;
-	struct hashmap *entries = NULL;
+	struct ext2fs_hashmap *entries = NULL;
 	struct basefs_entry *entry;
 	FILE *f = basefs_open(file);
 	if (!f)
 		return NULL;
-	entries = hashmap_create(djb2_hash, free_base_fs_entry, 1024);
+	entries = ext2fs_hashmap_create(ext2fs_djb2_hash, free_base_fs_entry, 1024);
 	if (!entries)
 		goto end;
 
 	while ((entry = basefs_readline(f, mountpoint, &err)))
-		hashmap_add(entries, entry, entry->path);
+		ext2fs_hashmap_add(entries, entry, entry->path,
+				   strlen(entry->path));
 
 	if (err) {
 		fclose(f);
-		hashmap_free(entries);
+		ext2fs_hashmap_free(entries);
 		return NULL;
 	}
 end:
diff --git a/contrib/android/base_fs.h b/contrib/android/base_fs.h
index 94bae29..e9f46b4 100644
--- a/contrib/android/base_fs.h
+++ b/contrib/android/base_fs.h
@@ -13,6 +13,6 @@
 
 extern struct fsmap_format base_fs_format;
 
-struct hashmap *basefs_parse(const char *file, const char *mountpoint);
+struct ext2fs_hashmap *basefs_parse(const char *file, const char *mountpoint);
 
 #endif /* !BASE_FS_H */
diff --git a/contrib/android/basefs_allocator.c b/contrib/android/basefs_allocator.c
index 3d014a2..c44532f 100644
--- a/contrib/android/basefs_allocator.c
+++ b/contrib/android/basefs_allocator.c
@@ -6,7 +6,7 @@
 #include "base_fs.h"
 
 struct base_fs_allocator {
-	struct hashmap *entries;
+	struct ext2fs_hashmap *entries;
 	struct basefs_entry *cur_entry;
 };
 
@@ -36,9 +36,9 @@
 {
 	errcode_t retval;
 	struct basefs_entry *e;
-	struct hashmap_entry *it = NULL;
+	struct ext2fs_hashmap_entry *it = NULL;
 	struct base_fs_allocator *allocator;
-	struct hashmap *entries = basefs_parse(file, mountpoint);
+	struct ext2fs_hashmap *entries = basefs_parse(file, mountpoint);
 	if (!entries)
 		return -1;
 
@@ -49,7 +49,7 @@
 	retval = ext2fs_read_bitmaps(fs);
 	if (retval)
 		goto err_bitmap;
-	while ((e = hashmap_iter_in_order(entries, &it)))
+	while ((e = ext2fs_hashmap_iter_in_order(entries, &it)))
 		fs_reserve_blocks_range(fs, e->head);
 
 	allocator->cur_entry = NULL;
@@ -64,7 +64,7 @@
 err_bitmap:
 	free(allocator);
 err_alloc:
-	hashmap_free(entries);
+	ext2fs_hashmap_free(entries);
 	return EXIT_FAILURE;
 }
 
@@ -97,10 +97,10 @@
 void base_fs_alloc_cleanup(ext2_filsys fs)
 {
 	struct basefs_entry *e;
-	struct hashmap_entry *it = NULL;
+	struct ext2fs_hashmap_entry *it = NULL;
 	struct base_fs_allocator *allocator = fs->priv_data;
 
-	while ((e = hashmap_iter_in_order(allocator->entries, &it))) {
+	while ((e = ext2fs_hashmap_iter_in_order(allocator->entries, &it))) {
 		fs_free_blocks_range(fs, e->head);
 		delete_block_ranges(e->head);
 		e->head = e->tail = NULL;
@@ -108,7 +108,7 @@
 
 	fs->priv_data = NULL;
 	fs->get_alloc_block2 = NULL;
-	hashmap_free(allocator->entries);
+	ext2fs_hashmap_free(allocator->entries);
 	free(allocator);
 }
 
@@ -123,8 +123,9 @@
 		return 0;
 
 	if (allocator)
-		allocator->cur_entry = hashmap_lookup(allocator->entries,
-						      target_path);
+		allocator->cur_entry = ext2fs_hashmap_lookup(allocator->entries,
+						      target_path,
+						      strlen(target_path));
 	return 0;
 }
 
diff --git a/contrib/android/e2fsdroid.c b/contrib/android/e2fsdroid.c
index c73b0be..2fe922d 100644
--- a/contrib/android/e2fsdroid.c
+++ b/contrib/android/e2fsdroid.c
@@ -32,7 +32,7 @@
 {
 	fprintf(stderr, "%s [-B block_list] [-D basefs_out] [-T timestamp]\n"
 			"\t[-C fs_config] [-S file_contexts] [-p product_out]\n"
-			"\t[-a mountpoint] [-d basefs_in] [-f src_dir] [-e] image\n",
+			"\t[-a mountpoint] [-d basefs_in] [-f src_dir] [-e] [-s] image\n",
                 prog_name);
 	exit(ret);
 }
@@ -73,7 +73,7 @@
 
 	add_error_table(&et_ext2_error_table);
 
-	while ((c = getopt (argc, argv, "T:C:S:p:a:D:d:B:f:e")) != EOF) {
+	while ((c = getopt (argc, argv, "T:C:S:p:a:D:d:B:f:es")) != EOF) {
 		switch (c) {
 		case 'T':
 			fixed_time = strtoul(optarg, &p, 0);
@@ -119,6 +119,9 @@
 		case 'e':
 			android_sparse_file = 0;
 			break;
+		case 's':
+			flags |= EXT2_FLAG_SHARE_DUP;
+			break;
 		default:
 			usage(EXIT_FAILURE);
 		}
diff --git a/contrib/android/hashmap.c b/contrib/android/hashmap.c
deleted file mode 100644
index eee0071..0000000
--- a/contrib/android/hashmap.c
+++ /dev/null
@@ -1,76 +0,0 @@
-#include "hashmap.h"
-#include <string.h>
-
-uint32_t djb2_hash(const void *str)
-{
-	int c;
-	const char *s = str;
-	uint32_t hash = 5381;
-
-	while ((c = *s++))
-		hash = ((hash << 5) + hash) + c;
-	return hash;
-}
-
-struct hashmap *hashmap_create(uint32_t(*hash_fct)(const void*),
-			       void(*free_fct)(void*), size_t size)
-{
-	struct hashmap *h = calloc(sizeof(struct hashmap) +
-				      sizeof(struct hashmap_entry) * size, 1);
-	h->size = size;
-	h->free = free_fct;
-	h->hash = hash_fct;
-	h->first = h->last = NULL;
-	return h;
-}
-
-void hashmap_add(struct hashmap *h, void *data, const void *key)
-{
-	uint32_t hash = h->hash(key) % h->size;
-	struct hashmap_entry *e = malloc(sizeof(*e));
-
-	e->data = data;
-	e->key = key;
-	e->next = h->entries[hash];
-	h->entries[hash] = e;
-
-	e->list_prev = NULL;
-	e->list_next = h->first;
-	if (h->first)
-		h->first->list_prev = e;
-	h->first = e;
-	if (!h->last)
-		h->last = e;
-}
-
-void *hashmap_lookup(struct hashmap *h, const void *key)
-{
-	struct hashmap_entry *iter;
-	uint32_t hash = h->hash(key) % h->size;
-
-	for (iter = h->entries[hash]; iter; iter = iter->next)
-		if (!strcmp(iter->key, key))
-			return iter->data;
-	return NULL;
-}
-
-void *hashmap_iter_in_order(struct hashmap *h, struct hashmap_entry **it)
-{
-	*it = *it ? (*it)->list_next : h->first;
-	return *it ? (*it)->data : NULL;
-}
-
-void hashmap_free(struct hashmap *h)
-{
-	for (size_t i = 0; i < h->size; ++i) {
-		struct hashmap_entry *it = h->entries[i];
-		while (it) {
-			struct hashmap_entry *tmp = it->next;
-			if (h->free)
-				h->free(it->data);
-			free(it);
-			it = tmp;
-		}
-	}
-	free(h);
-}
diff --git a/contrib/android/hashmap.h b/contrib/android/hashmap.h
deleted file mode 100644
index 70d0ed1..0000000
--- a/contrib/android/hashmap.h
+++ /dev/null
@@ -1,32 +0,0 @@
-#ifndef HASHMAP_H
-# define HASHMAP_H
-
-# include <stdlib.h>
-# include <stdint.h>
-
-struct hashmap {
-	uint32_t size;
-	uint32_t(*hash)(const void *key);
-	void(*free)(void*);
-	struct hashmap_entry *first;
-	struct hashmap_entry *last;
-	struct hashmap_entry {
-		void *data;
-		const void *key;
-		struct hashmap_entry *next;
-		struct hashmap_entry *list_next;
-		struct hashmap_entry *list_prev;
-	} *entries[0];
-};
-
-struct hashmap *hashmap_create(uint32_t(*hash_fct)(const void*),
-			       void(*free_fct)(void*), size_t size);
-void hashmap_add(struct hashmap *h, void *data, const void *key);
-void *hashmap_lookup(struct hashmap *h, const void *key);
-void *hashmap_iter_in_order(struct hashmap *h, struct hashmap_entry **it);
-void hashmap_del(struct hashmap *h, struct hashmap_entry *e);
-void hashmap_free(struct hashmap *h);
-
-uint32_t djb2_hash(const void *str);
-
-#endif /* !HASHMAP_H */
diff --git a/lib/e2p/feature.c b/lib/e2p/feature.c
index b7f6c1d..0fab9c7 100644
--- a/lib/e2p/feature.c
+++ b/lib/e2p/feature.c
@@ -72,6 +72,8 @@
 			"read-only" },
 	{	E2P_FEATURE_RO_INCOMPAT, EXT4_FEATURE_RO_COMPAT_PROJECT,
 			"project"},
+	{	E2P_FEATURE_RO_INCOMPAT, EXT4_FEATURE_RO_COMPAT_SHARED_BLOCKS,
+			"shared_blocks"},
 
 	{	E2P_FEATURE_INCOMPAT, EXT2_FEATURE_INCOMPAT_COMPRESSION,
 			"compression" },
diff --git a/lib/ext2fs/Android.bp b/lib/ext2fs/Android.bp
index 427d93b..06a750e 100644
--- a/lib/ext2fs/Android.bp
+++ b/lib/ext2fs/Android.bp
@@ -47,6 +47,7 @@
         "get_pathname.c",
         "getsize.c",
         "getsectsize.c",
+        "hashmap.c",
         "i_block.c",
         "icount.c",
         "imager.c",
diff --git a/lib/ext2fs/ext2_fs.h b/lib/ext2fs/ext2_fs.h
index 27a7d3a..ab1db6e 100644
--- a/lib/ext2fs/ext2_fs.h
+++ b/lib/ext2fs/ext2_fs.h
@@ -812,6 +812,7 @@
 #define EXT4_FEATURE_RO_COMPAT_REPLICA		0x0800
 #define EXT4_FEATURE_RO_COMPAT_READONLY		0x1000
 #define EXT4_FEATURE_RO_COMPAT_PROJECT		0x2000 /* Project quota */
+#define EXT4_FEATURE_RO_COMPAT_SHARED_BLOCKS	0x4000
 
 
 #define EXT2_FEATURE_INCOMPAT_COMPRESSION	0x0001
@@ -904,6 +905,7 @@
 EXT4_FEATURE_RO_COMPAT_FUNCS(replica,		4, REPLICA)
 EXT4_FEATURE_RO_COMPAT_FUNCS(readonly,		4, READONLY)
 EXT4_FEATURE_RO_COMPAT_FUNCS(project,		4, PROJECT)
+EXT4_FEATURE_RO_COMPAT_FUNCS(shared_blocks,	4, SHARED_BLOCKS)
 
 EXT4_FEATURE_INCOMPAT_FUNCS(compression,	2, COMPRESSION)
 EXT4_FEATURE_INCOMPAT_FUNCS(filetype,		2, FILETYPE)
diff --git a/lib/ext2fs/ext2fs.h b/lib/ext2fs/ext2fs.h
index e153c81..470e7d7 100644
--- a/lib/ext2fs/ext2fs.h
+++ b/lib/ext2fs/ext2fs.h
@@ -94,6 +94,8 @@
 #include <ext2fs/ext2_ext_attr.h>
 #endif
 
+#include "hashmap.h"
+
 /*
  * Portability help for Microsoft Visual C++
  */
@@ -195,6 +197,7 @@
 #define EXT2_FLAG_DIRECT_IO		0x80000
 #define EXT2_FLAG_SKIP_MMP		0x100000
 #define EXT2_FLAG_IGNORE_CSUM_ERRORS	0x200000
+#define EXT2_FLAG_SHARE_DUP		0x400000
 
 /*
  * Special flag in the ext2 inode i_flag field that means that this is
@@ -295,6 +298,9 @@
 			       blk64_t len, blk64_t *pblk, blk64_t *plen);
 	void (*block_alloc_stats_range)(ext2_filsys fs, blk64_t blk, blk_t num,
 					int inuse);
+
+	/* hashmap for SHA of data blocks */
+	struct ext2fs_hashmap* block_sha_map;
 };
 
 #if EXT2_FLAT_INCLUDES
@@ -614,7 +620,8 @@
 					 EXT4_FEATURE_RO_COMPAT_QUOTA|\
 					 EXT4_FEATURE_RO_COMPAT_METADATA_CSUM|\
 					 EXT4_FEATURE_RO_COMPAT_READONLY |\
-					 EXT4_FEATURE_RO_COMPAT_PROJECT)
+					 EXT4_FEATURE_RO_COMPAT_PROJECT |\
+					 EXT4_FEATURE_RO_COMPAT_SHARED_BLOCKS)
 
 /*
  * These features are only allowed if EXT2_FLAG_SOFTSUPP_FEATURES is passed
diff --git a/lib/ext2fs/fileio.c b/lib/ext2fs/fileio.c
index 810a7fd..5bc02d0 100644
--- a/lib/ext2fs/fileio.c
+++ b/lib/ext2fs/fileio.c
@@ -32,6 +32,12 @@
 	char 			*buf;
 };
 
+struct block_entry {
+	blk64_t		physblock;
+	unsigned char 	sha[EXT2FS_SHA512_LENGTH];
+};
+typedef struct block_entry *block_entry_t;
+
 #define BMAP_BUFFER (file->buf + fs->blocksize)
 
 errcode_t ext2fs_file_open2(ext2_filsys fs, ext2_ino_t ino,
@@ -389,6 +395,8 @@
 	errcode_t	retval = 0;
 	unsigned int	start, c, count = 0;
 	const char	*ptr = (const char *) buf;
+	block_entry_t	new_block = NULL, old_block = NULL;
+	int		bmap_flags = 0;
 
 	EXT2_CHECK_MAGIC(file, EXT2_ET_MAGIC_EXT2_FILE);
 	fs = file->fs;
@@ -424,22 +432,51 @@
 		if (retval)
 			goto fail;
 
+		file->flags |= EXT2_FILE_BUF_DIRTY;
+		memcpy(file->buf+start, ptr, c);
+
 		/*
 		 * OK, the physical block hasn't been allocated yet.
 		 * Allocate it.
 		 */
 		if (!file->physblock) {
+			bmap_flags = (file->ino ? BMAP_ALLOC : 0);
+			if (fs->flags & EXT2_FLAG_SHARE_DUP) {
+				new_block = calloc(1, sizeof(*new_block));
+				if (!new_block) {
+					retval = EXT2_ET_NO_MEMORY;
+					goto fail;
+				}
+				ext2fs_sha512((const unsigned char*)file->buf,
+						fs->blocksize, new_block->sha);
+				old_block = ext2fs_hashmap_lookup(
+							fs->block_sha_map,
+							new_block->sha,
+							sizeof(new_block->sha));
+			}
+
+			if (old_block) {
+				file->physblock = old_block->physblock;
+				bmap_flags |= BMAP_SET;
+				free(new_block);
+				new_block = NULL;
+			}
+
 			retval = ext2fs_bmap2(fs, file->ino, &file->inode,
 					      BMAP_BUFFER,
-					      file->ino ? BMAP_ALLOC : 0,
+					      bmap_flags,
 					      file->blockno, 0,
 					      &file->physblock);
 			if (retval)
 				goto fail;
+
+			if (new_block) {
+				new_block->physblock = file->physblock;
+				ext2fs_hashmap_add(fs->block_sha_map, new_block,
+					new_block->sha, sizeof(new_block->sha));
+			}
 		}
 
-		file->flags |= EXT2_FILE_BUF_DIRTY;
-		memcpy(file->buf+start, ptr, c);
 		file->pos += c;
 		ptr += c;
 		count += c;
diff --git a/lib/ext2fs/freefs.c b/lib/ext2fs/freefs.c
index ea9742e..68b8e9a 100644
--- a/lib/ext2fs/freefs.c
+++ b/lib/ext2fs/freefs.c
@@ -17,6 +17,7 @@
 
 #include "ext2_fs.h"
 #include "ext2fsP.h"
+#include "hashmap.h"
 
 void ext2fs_free(ext2_filsys fs)
 {
@@ -59,6 +60,9 @@
 	if (fs->mmp_cmp)
 		ext2fs_free_mem(&fs->mmp_cmp);
 
+	if (fs->block_sha_map)
+		ext2fs_hashmap_free(fs->block_sha_map);
+
 	fs->magic = 0;
 
 	ext2fs_zero_blocks2(NULL, 0, 0, NULL, NULL);
diff --git a/lib/ext2fs/hashmap.c b/lib/ext2fs/hashmap.c
new file mode 100644
index 0000000..ade5d89
--- /dev/null
+++ b/lib/ext2fs/hashmap.c
@@ -0,0 +1,83 @@
+#include "hashmap.h"
+#include <string.h>
+
+uint32_t ext2fs_djb2_hash(const void *str, size_t size)
+{
+	int c;
+	const char *s = str;
+	uint32_t hash = 5381;
+
+	while (size-- > 0) {
+		c = *s++;
+		hash = ((hash << 5) + hash) + c;
+	}
+	return hash;
+}
+
+struct ext2fs_hashmap *ext2fs_hashmap_create(
+				uint32_t(*hash_fct)(const void*, size_t),
+				void(*free_fct)(void*), size_t size)
+{
+	struct ext2fs_hashmap *h = calloc(sizeof(struct ext2fs_hashmap) +
+				sizeof(struct ext2fs_hashmap_entry) * size, 1);
+	h->size = size;
+	h->free = free_fct;
+	h->hash = hash_fct;
+	h->first = h->last = NULL;
+	return h;
+}
+
+void ext2fs_hashmap_add(struct ext2fs_hashmap *h, void *data, const void *key,
+			size_t key_len)
+{
+	uint32_t hash = h->hash(key, key_len) % h->size;
+	struct ext2fs_hashmap_entry *e = malloc(sizeof(*e));
+
+	e->data = data;
+	e->key = key;
+	e->key_len = key_len;
+	e->next = h->entries[hash];
+	h->entries[hash] = e;
+
+	e->list_prev = NULL;
+	e->list_next = h->first;
+	if (h->first)
+		h->first->list_prev = e;
+	h->first = e;
+	if (!h->last)
+		h->last = e;
+}
+
+void *ext2fs_hashmap_lookup(struct ext2fs_hashmap *h, const void *key,
+			    size_t key_len)
+{
+	struct ext2fs_hashmap_entry *iter;
+	uint32_t hash = h->hash(key, key_len) % h->size;
+
+	for (iter = h->entries[hash]; iter; iter = iter->next)
+		if (iter->key_len == key_len && !memcmp(iter->key, key, key_len))
+			return iter->data;
+	return NULL;
+}
+
+void *ext2fs_hashmap_iter_in_order(struct ext2fs_hashmap *h,
+				   struct ext2fs_hashmap_entry **it)
+{
+	*it = *it ? (*it)->list_next : h->first;
+	return *it ? (*it)->data : NULL;
+}
+
+void ext2fs_hashmap_free(struct ext2fs_hashmap *h)
+{
+	for (size_t i = 0; i < h->size; ++i) {
+		struct ext2fs_hashmap_entry *it = h->entries[i];
+		while (it) {
+			struct ext2fs_hashmap_entry *tmp = it->next;
+			if (h->free)
+				h->free(it->data);
+			free(it);
+			it = tmp;
+		}
+	}
+	free(h);
+}
diff --git a/lib/ext2fs/hashmap.h b/lib/ext2fs/hashmap.h
new file mode 100644
index 0000000..7127186
--- /dev/null
+++ b/lib/ext2fs/hashmap.h
@@ -0,0 +1,38 @@
+#ifndef HASHMAP_H
+# define HASHMAP_H
+
+# include <stdlib.h>
+# include <stdint.h>
+
+struct ext2fs_hashmap {
+	uint32_t size;
+	uint32_t(*hash)(const void *key, size_t len);
+	void(*free)(void*);
+	struct ext2fs_hashmap_entry *first;
+	struct ext2fs_hashmap_entry *last;
+	struct ext2fs_hashmap_entry {
+		void *data;
+		const void *key;
+		size_t key_len;
+		struct ext2fs_hashmap_entry *next;
+		struct ext2fs_hashmap_entry *list_next;
+		struct ext2fs_hashmap_entry *list_prev;
+	} *entries[0];
+};
+
+struct ext2fs_hashmap *ext2fs_hashmap_create(
+				uint32_t(*hash_fct)(const void*, size_t),
+				void(*free_fct)(void*), size_t size);
+void ext2fs_hashmap_add(struct ext2fs_hashmap *h, void *data, const void *key,
+			size_t key_len);
+void *ext2fs_hashmap_lookup(struct ext2fs_hashmap *h, const void *key,
+			    size_t key_len);
+void *ext2fs_hashmap_iter_in_order(struct ext2fs_hashmap *h,
+				   struct ext2fs_hashmap_entry **it);
+void ext2fs_hashmap_del(struct ext2fs_hashmap *h,
+			struct ext2fs_hashmap_entry *e);
+void ext2fs_hashmap_free(struct ext2fs_hashmap *h);
+
+uint32_t ext2fs_djb2_hash(const void *str, size_t size);
+
+#endif /* !HASHMAP_H */
diff --git a/lib/ext2fs/openfs.c b/lib/ext2fs/openfs.c
index 94d0ef1..43d68ad 100644
--- a/lib/ext2fs/openfs.c
+++ b/lib/ext2fs/openfs.c
@@ -94,6 +94,12 @@
 			    manager, ret_fs);
 }
 
+static void block_sha_map_free_entry(void *data)
+{
+    free(data);
+    return;
+}
+
 /*
  *  Note: if superblock is non-zero, block-size must also be non-zero.
  * 	Superblock and block_size can be zero to use the default size.
@@ -474,6 +480,16 @@
 		}
 	}
 
+	if (fs->flags & EXT2_FLAG_SHARE_DUP) {
+		fs->block_sha_map = ext2fs_hashmap_create(ext2fs_djb2_hash,
+					block_sha_map_free_entry, 4096);
+		if (!fs->block_sha_map) {
+			retval = EXT2_ET_NO_MEMORY;
+			goto cleanup;
+		}
+		ext2fs_set_feature_shared_blocks(fs->super);
+	}
+
 	fs->flags &= ~EXT2_FLAG_NOFREE_ON_ERROR;
 	*ret_fs = fs;