[PATCH v3 0/5] btrfs: add per-inode compression levels in xattrs

[PATCH v3 0/5] btrfs: add per-inode compression levels in xattrs

[koraynilay]

Add per-inode compression levels using
btrfs property set /path/to/file compression "algo:level", using the
same syntax as the compress mount option.
If set on folders, all new children will inherit the setting, while
already existing children will be unaffected.

This patch series also fixes a small bug: before, when setting
btrfs.compression, it would keep the mount option level, even if the
algo was different (!!), so with e.g. compress=zstd:15 and
btrfs.compression=zlib the data gets compressed at zlib:9 (because it
would still get clamped at the right range); now if the level isn't
explicitly set it will use the default level for the algo.

I also wanna thank Zygo for helping me by explaining stuff and for
noticing this bug.

Changes in this v3:
* the first patch contains only the bugfix for the mentioned bug, so it
  can be backported to older kernels if needed;
* fix a bisection and compilation error.

koraynilay (5):
  btrfs: fix -o compress= level getting inherited by compression xattr
    property
  btrfs: export btrfs_match_compress_type(), move it to compression.h
  btrfs: also validate compression levels in
    btrfs_compress_is_valid_type()
  btrfs: add per-inode compression levels in xattrs
  btrfs: support inheritance for per-inode compression levels

 fs/btrfs/btrfs_inode.h |  1 +
 fs/btrfs/compression.c | 35 ++++++++++++++++++++--
 fs/btrfs/compression.h |  3 +-
 fs/btrfs/inode.c       |  2 ++
 fs/btrfs/props.c       | 66 ++++++++++++++++++++++++++++++++++--------
 fs/btrfs/super.c       |  8 -----
 6 files changed, 91 insertions(+), 24 deletions(-)


base-commit: a13307e97d5c54b65720bb71fa379960ded1e51a
-- 
2.55.0

[PATCH v3 1/5] btrfs: fix -o compress= level getting inherited by compression xattr property

[koraynilay]

When setting the btrfs.compression xattr, btrfs uses the mount option level
(since levels in the xattr aren't supported yet) to compress the data, even
if the compression algorithm between the property and the compress= option
are different (!!).
For example, when mounting with compress=zstd:15 and setting
btrfs.compression=zlib, the data would get compressed at zlib:9, because
btrfs would take "zlib" from the xattr but "15" from the mount option,
which would then get correctly clamped at 9.

To fix, just hard-code the compress level at 0, forcing the property's
algorithm default.

Reported-by: Zygo Blaxell <ce3g8jdj@umail.furryterror.org>
Signed-off-by: koraynilay <koray.fra@gmail.com>
---
 fs/btrfs/inode.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
index 2534cd9284d5..6d7f2aa2555c 100644
--- a/fs/btrfs/inode.c
+++ b/fs/btrfs/inode.c
@@ -938,6 +938,7 @@ static void compress_file_range(struct btrfs_work *work)
 		compress_level = inode->defrag_compress_level;
 	} else if (inode->prop_compress) {
 		compress_type = inode->prop_compress;
+		compress_level = 0;
 	}
 
 	/* Compression level is applied here. */
@@ -2326,6 +2327,7 @@ static int run_delalloc_inline(struct btrfs_inode *inode, struct folio *locked_f
 			compress_level = inode->defrag_compress_level;
 		} else if (inode->prop_compress) {
 			compress_type = inode->prop_compress;
+			compress_level = 0;
 		}
 		cb = btrfs_compress_bio(inode, 0, blocksize, compress_type, compress_level, 0);
 		if (IS_ERR(cb)) {
-- 
2.55.0

Re: [PATCH v3 1/5] btrfs: fix -o compress= level getting inherited by compression xattr property

[Zygo Blaxell]

On Sun, Aug 09, 2026 at 08:52:59PM +0200, koraynilay wrote:
> When setting the btrfs.compression xattr, btrfs uses the mount option level
> (since levels in the xattr aren't supported yet) to compress the data, even
> if the compression algorithm between the property and the compress= option
> are different (!!).
> For example, when mounting with compress=zstd:15 and setting
> btrfs.compression=zlib, the data would get compressed at zlib:9, because
> btrfs would take "zlib" from the xattr but "15" from the mount option,
> which would then get correctly clamped at 9.
> 
> To fix, just hard-code the compress level at 0, forcing the property's
> algorithm default.
> 
> Reported-by: Zygo Blaxell <ce3g8jdj@umail.furryterror.org>
> Signed-off-by: koraynilay <koray.fra@gmail.com>
> ---
>  fs/btrfs/inode.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
> index 2534cd9284d5..6d7f2aa2555c 100644
> --- a/fs/btrfs/inode.c
> +++ b/fs/btrfs/inode.c
> @@ -938,6 +938,7 @@ static void compress_file_range(struct btrfs_work *work)
>  		compress_level = inode->defrag_compress_level;
>  	} else if (inode->prop_compress) {
>  		compress_type = inode->prop_compress;
> +		compress_level = 0;

This set to zero should be conditional on inode->prop_compress !=
fs_info->compress_type; otherwise, it prevents the compress-level mount
option from working in the common case where 'btrfs.compression=zstd'
or 'chattr +c' has been set.

>  	}
>  
>  	/* Compression level is applied here. */
> @@ -2326,6 +2327,7 @@ static int run_delalloc_inline(struct btrfs_inode *inode, struct folio *locked_f
>  			compress_level = inode->defrag_compress_level;
>  		} else if (inode->prop_compress) {
>  			compress_type = inode->prop_compress;
> +			compress_level = 0;
>  		}
>  		cb = btrfs_compress_bio(inode, 0, blocksize, compress_type, compress_level, 0);
>  		if (IS_ERR(cb)) {
> -- 
> 2.55.0
> 
> 

Re: [PATCH v3 1/5] btrfs: fix -o compress= level getting inherited by compression xattr property

[Qu Wenruo]

在 2026/8/10 05:45, Zygo Blaxell 写道:
> On Sun, Aug 09, 2026 at 08:52:59PM +0200, koraynilay wrote:
>> When setting the btrfs.compression xattr, btrfs uses the mount option level
>> (since levels in the xattr aren't supported yet) to compress the data, even
>> if the compression algorithm between the property and the compress= option
>> are different (!!).
>> For example, when mounting with compress=zstd:15 and setting
>> btrfs.compression=zlib, the data would get compressed at zlib:9, because
>> btrfs would take "zlib" from the xattr but "15" from the mount option,
>> which would then get correctly clamped at 9.
>>
>> To fix, just hard-code the compress level at 0, forcing the property's
>> algorithm default.
>>
>> Reported-by: Zygo Blaxell <ce3g8jdj@umail.furryterror.org>
>> Signed-off-by: koraynilay <koray.fra@gmail.com>
>> ---
>>   fs/btrfs/inode.c | 2 ++
>>   1 file changed, 2 insertions(+)
>>
>> diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
>> index 2534cd9284d5..6d7f2aa2555c 100644
>> --- a/fs/btrfs/inode.c
>> +++ b/fs/btrfs/inode.c
>> @@ -938,6 +938,7 @@ static void compress_file_range(struct btrfs_work *work)
>>   		compress_level = inode->defrag_compress_level;
>>   	} else if (inode->prop_compress) {
>>   		compress_type = inode->prop_compress;
>> +		compress_level = 0;
> 
> This set to zero should be conditional on inode->prop_compress !=
> fs_info->compress_type; otherwise, it prevents the compress-level mount
> option from working in the common case where 'btrfs.compression=zstd'
> or 'chattr +c' has been set.

No, read this discussion.

https://lore.kernel.org/linux-btrfs/DKK0XWCI89MM.2G6KD41GSR46J@gmail.com/T/#m79e6c1ecbcc61ebb57dca5cbb3eceabd052ecdbc

> 
>>   	}
>>   
>>   	/* Compression level is applied here. */
>> @@ -2326,6 +2327,7 @@ static int run_delalloc_inline(struct btrfs_inode *inode, struct folio *locked_f
>>   			compress_level = inode->defrag_compress_level;
>>   		} else if (inode->prop_compress) {
>>   			compress_type = inode->prop_compress;
>> +			compress_level = 0;
>>   		}
>>   		cb = btrfs_compress_bio(inode, 0, blocksize, compress_type, compress_level, 0);
>>   		if (IS_ERR(cb)) {
>> -- 
>> 2.55.0
>>
>>

[PATCH v3 2/5] btrfs: export btrfs_match_compress_type(), move it to compression.h

[koraynilay]

Export btrfs_match_compress_type() from being a static and locally used
function in super.c and move it to compression.c, exporting it in
compression.h.  This allows it to be used in the next patches as
validation for compression algorithm names.

Assisted-by: Gemini:3.1-pro antigravity-cli-1.1.5
Signed-off-by: koraynilay <koray.fra@gmail.com>
---
 fs/btrfs/compression.c | 17 +++++++++++++++++
 fs/btrfs/compression.h |  1 +
 fs/btrfs/super.c       |  8 --------
 3 files changed, 18 insertions(+), 8 deletions(-)

diff --git a/fs/btrfs/compression.c b/fs/btrfs/compression.c
index ffb6b52863a7..58138f300b58 100644
--- a/fs/btrfs/compression.c
+++ b/fs/btrfs/compression.c
@@ -1660,3 +1660,20 @@ int btrfs_compress_str2level(unsigned int type, const char *str, int *level_ret)
 	*level_ret = btrfs_compress_set_level(type, level);
 	return 0;
 }
+
+/**
+ * btrfs_match_compress_type - Check if the string matches the compression type
+ * @string:         The string to check
+ * @type:           The compression type string (name) to match against (e.g. "zstd")
+ * @may_have_level: If true, the string may have a level suffix (e.g., ":1")
+ *
+ * Return: %true if the string matches the type and, if %may_have_level is %true,
+ * has a level suffix, %false otherwise.
+ */
+bool btrfs_match_compress_type(const char *string, const char *type, bool may_have_level)
+{
+	const int len = strlen(type);
+
+	return (strncmp(string, type, len) == 0) &&
+		((may_have_level && string[len] == ':') || string[len] == '\0');
+}
diff --git a/fs/btrfs/compression.h b/fs/btrfs/compression.h
index 1022dc53ec51..e67ba47b4cdc 100644
--- a/fs/btrfs/compression.h
+++ b/fs/btrfs/compression.h
@@ -97,6 +97,7 @@ void btrfs_submit_compressed_write(struct btrfs_ordered_extent *ordered,
 void btrfs_submit_compressed_read(struct btrfs_bio *bbio);
 
 int btrfs_compress_str2level(unsigned int type, const char *str, int *level_ret);
+bool btrfs_match_compress_type(const char *string, const char *type, bool may_have_level);
 
 struct folio *btrfs_alloc_compr_folio(struct btrfs_fs_info *fs_info, gfp_t gfp);
 void btrfs_free_compr_folio(struct folio *folio);
diff --git a/fs/btrfs/super.c b/fs/btrfs/super.c
index f4e34898d581..7a21085c33c5 100644
--- a/fs/btrfs/super.c
+++ b/fs/btrfs/super.c
@@ -264,14 +264,6 @@ static const struct fs_parameter_spec btrfs_fs_parameters[] = {
 	{}
 };
 
-static bool btrfs_match_compress_type(const char *string, const char *type, bool may_have_level)
-{
-	const int len = strlen(type);
-
-	return (strncmp(string, type, len) == 0) &&
-		((may_have_level && string[len] == ':') || string[len] == '\0');
-}
-
 static int btrfs_parse_compress(struct btrfs_fs_context *ctx,
 				const struct fs_parameter *param, int opt)
 {
-- 
2.55.0

[PATCH v3 3/5] btrfs: also validate compression levels in btrfs_compress_is_valid_type()

[koraynilay]

Change btrfs_compress_is_valid_type() to use btrfs_match_compress_type()
and btrfs_compress_str2level() instead of a simple strncmp(), which would
validate even incorrect strings (e.g. "zstd:invalid" or "zstdinvalid").

This also makes the function validate levels in the same way the
compress= option gets parsed, allowing bigger or smaller values, but
still clamping them to the min or max supported.

Furthermore, remove the len parameter, since now it requires a
NUL-terminated string because of btrfs_compress_str2level(); this change
is fine because btrfs_compress_is_valid_type() is used only once in
props.c by prop_compression_validate(), which now uses kmemdup_nul() to
convert the user-supplied xattr value to a NUL-terminated string.

Assisted-by: Gemini:3.1-pro antigravity-cli-1.1.5
Signed-off-by: koraynilay <koray.fra@gmail.com>
---
 fs/btrfs/compression.c | 18 +++++++++++++++---
 fs/btrfs/compression.h |  2 +-
 fs/btrfs/props.c       | 16 ++++++++++++----
 3 files changed, 28 insertions(+), 8 deletions(-)

diff --git a/fs/btrfs/compression.c b/fs/btrfs/compression.c
index 58138f300b58..e723cef3b5dc 100644
--- a/fs/btrfs/compression.c
+++ b/fs/btrfs/compression.c
@@ -70,18 +70,30 @@ static struct compressed_bio *alloc_compressed_bio(struct btrfs_inode *inode,
 	return to_compressed_bio(bbio);
 }
 
-bool btrfs_compress_is_valid_type(const char *str, size_t len)
+/**
+ * btrfs_compress_is_valid_type - Check if a string is a valid compression type.
+ * @str: The compression string to check. Must be null-terminated.
+ *
+ * Return: %true if the string is a valid compression algorithm (optionally with
+ * a level suffix, e.g. "zstd" or "zstd:9"), %false otherwise.
+ */
+bool btrfs_compress_is_valid_type(const char *str)
 {
+	size_t len = strlen(str);
 	int i;
 
 	for (i = 1; i < ARRAY_SIZE(btrfs_compress_types); i++) {
 		size_t comp_len = strlen(btrfs_compress_types[i]);
+		const char *comp_type = btrfs_compress_types[i];
+		int tmp_level;
 
 		if (len < comp_len)
 			continue;
 
-		if (!strncmp(btrfs_compress_types[i], str, comp_len))
-			return true;
+		if (btrfs_match_compress_type(str, comp_type, true)) {
+			if (btrfs_compress_str2level(i, str + comp_len, &tmp_level) == 0)
+				return true;
+		}
 	}
 	return false;
 }
diff --git a/fs/btrfs/compression.h b/fs/btrfs/compression.h
index e67ba47b4cdc..c63bed9f4152 100644
--- a/fs/btrfs/compression.h
+++ b/fs/btrfs/compression.h
@@ -132,7 +132,7 @@ extern const struct btrfs_compress_levels btrfs_lzo_compress;
 extern const struct btrfs_compress_levels btrfs_zstd_compress;
 
 const char* btrfs_compress_type2str(enum btrfs_compression_type type);
-bool btrfs_compress_is_valid_type(const char *str, size_t len);
+bool btrfs_compress_is_valid_type(const char *str);
 
 int btrfs_compress_heuristic(struct btrfs_inode *inode, u64 start, u64 end);
 
diff --git a/fs/btrfs/props.c b/fs/btrfs/props.c
index bb77d46376d4..a269124c3b92 100644
--- a/fs/btrfs/props.c
+++ b/fs/btrfs/props.c
@@ -295,20 +295,28 @@ int btrfs_load_inode_props(struct btrfs_inode *inode, struct btrfs_path *path)
 static int prop_compression_validate(const struct btrfs_inode *inode,
 				     const char *value, size_t len)
 {
+	int ret = -EINVAL;
+	const char *value_str;
+
 	if (!btrfs_inode_can_compress(inode))
 		return -EINVAL;
 
 	if (!value)
 		return 0;
 
-	if (btrfs_compress_is_valid_type(value, len))
-		return 0;
-
 	if ((len == 2 && strncmp("no", value, 2) == 0) ||
 	    (len == 4 && strncmp("none", value, 4) == 0))
 		return 0;
 
-	return -EINVAL;
+	value_str = kmemdup_nul(value, len, GFP_KERNEL);
+	if (!value_str)
+		return -ENOMEM;
+
+	if (btrfs_compress_is_valid_type(value_str))
+		ret = 0;
+
+	kfree(value_str);
+	return ret;
 }
 
 static int prop_compression_apply(struct btrfs_inode *inode, const char *value,
-- 
2.55.0

[PATCH v3 4/5] btrfs: add per-inode compression levels in xattrs

[koraynilay]

Add support for specifying algo:level using
btrfs property set /path/to/file compression "algo:level".

Add a signed 8 bit prop_compress_level property to btrfs_inode, which
can support from level -128 to 127, plenty for the currently supported
algo:level(s).

Change prop_compression_apply() to use the already present
btrfs_match_compress_type() and btrfs_compress_str2level() to parse the
xattr, using kmemdup_nul() to convert the user-supplied xattr value to a
NUL-terminated string to be used by btrfs_compress_str2level().

Assisted-by: Gemini:3.1-pro antigravity-cli-1.1.5
Signed-off-by: koraynilay <koray.fra@gmail.com>
---
 fs/btrfs/btrfs_inode.h |  1 +
 fs/btrfs/inode.c       |  4 ++--
 fs/btrfs/props.c       | 27 ++++++++++++++++++++++-----
 3 files changed, 25 insertions(+), 7 deletions(-)

diff --git a/fs/btrfs/btrfs_inode.h b/fs/btrfs/btrfs_inode.h
index 1082fa92c145..0a4e567d0109 100644
--- a/fs/btrfs/btrfs_inode.h
+++ b/fs/btrfs/btrfs_inode.h
@@ -130,6 +130,7 @@ struct btrfs_inode {
 
 	/* Cached value of inode property 'compression'. */
 	u8 prop_compress;
+	s8 prop_compress_level;
 
 	/*
 	 * Force compression on the file using the defrag ioctl, could be
diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
index 6d7f2aa2555c..cff4b3e97559 100644
--- a/fs/btrfs/inode.c
+++ b/fs/btrfs/inode.c
@@ -938,7 +938,7 @@ static void compress_file_range(struct btrfs_work *work)
 		compress_level = inode->defrag_compress_level;
 	} else if (inode->prop_compress) {
 		compress_type = inode->prop_compress;
-		compress_level = 0;
+		compress_level = inode->prop_compress_level;
 	}
 
 	/* Compression level is applied here. */
@@ -2327,7 +2327,7 @@ static int run_delalloc_inline(struct btrfs_inode *inode, struct folio *locked_f
 			compress_level = inode->defrag_compress_level;
 		} else if (inode->prop_compress) {
 			compress_type = inode->prop_compress;
-			compress_level = 0;
+			compress_level = inode->prop_compress_level;
 		}
 		cb = btrfs_compress_bio(inode, 0, blocksize, compress_type, compress_level, 0);
 		if (IS_ERR(cb)) {
diff --git a/fs/btrfs/props.c b/fs/btrfs/props.c
index a269124c3b92..f79a61a2759f 100644
--- a/fs/btrfs/props.c
+++ b/fs/btrfs/props.c
@@ -324,6 +324,9 @@ static int prop_compression_apply(struct btrfs_inode *inode, const char *value,
 {
 	struct btrfs_fs_info *fs_info = inode->root->fs_info;
 	int type;
+	int level = 0;
+	int ret = 0;
+	const char *value_str;
 
 	/* Reset to defaults */
 	if (len == 0) {
@@ -343,23 +346,37 @@ static int prop_compression_apply(struct btrfs_inode *inode, const char *value,
 		return 0;
 	}
 
-	if (!strncmp("lzo", value, 3)) {
+	value_str = kmemdup_nul(value, len, GFP_KERNEL);
+	if (!value_str)
+		return -ENOMEM;
+
+	if (btrfs_match_compress_type(value_str, "lzo", true)) {
 		type = BTRFS_COMPRESS_LZO;
 		btrfs_set_fs_incompat(fs_info, COMPRESS_LZO);
-	} else if (!strncmp("zlib", value, 4)) {
+	} else if (btrfs_match_compress_type(value_str, "zlib", true)) {
 		type = BTRFS_COMPRESS_ZLIB;
-	} else if (!strncmp("zstd", value, 4)) {
+		ret = btrfs_compress_str2level(type, value_str + 4, &level);
+		if (ret < 0)
+			goto out;
+	} else if (btrfs_match_compress_type(value_str, "zstd", true)) {
 		type = BTRFS_COMPRESS_ZSTD;
+		ret = btrfs_compress_str2level(type, value_str + 4, &level);
+		if (ret < 0)
+			goto out;
 		btrfs_set_fs_incompat(fs_info, COMPRESS_ZSTD);
 	} else {
-		return -EINVAL;
+		ret = -EINVAL;
+		goto out;
 	}
 
 	inode->flags &= ~BTRFS_INODE_NOCOMPRESS;
 	inode->flags |= BTRFS_INODE_COMPRESS;
 	inode->prop_compress = type;
+	inode->prop_compress_level = level;
 
-	return 0;
+out:
+	kfree(value_str);
+	return ret;
 }
 
 static bool prop_compression_ignore(const struct btrfs_inode *inode)
-- 
2.55.0

[PATCH v3 5/5] btrfs: support inheritance for per-inode compression levels

[koraynilay]

Change prop_handler's extract() signature to take an output buffer and
its length. This allows for the algo:level string to be generated
dynamically, but now the caller is in charge of managing that buffer
memory. Before this patch prop_compression_extract() would return only
the address of statically compiled string without being able to add the
level, now it concatenates the level to that statically compiled string.

This signature change is fine because the only currently supported prop
is compression, so there is only 1 extract() function.

Assisted-by: Gemini:3.1-pro antigravity-cli-1.1.5
Signed-off-by: koraynilay <koray.fra@gmail.com>
---
 fs/btrfs/props.c | 23 ++++++++++++++++++++---
 1 file changed, 20 insertions(+), 3 deletions(-)

diff --git a/fs/btrfs/props.c b/fs/btrfs/props.c
index f79a61a2759f..5ca728375d35 100644
--- a/fs/btrfs/props.c
+++ b/fs/btrfs/props.c
@@ -18,6 +18,15 @@
 #include "super.h"
 #include "dir-item.h"
 
+/*
+ * Max length of compression algorithm:level string.
+ *
+ * For now the longest possible string is "zstd:-15", which is
+ * 8 characters + 1 terminating null byte.
+ * Rounding it up to the closest power of 2 gives 16.
+ */
+#define BTRFS_COMPRESS_PROP_MAX_LEN 16
+
 #define BTRFS_PROP_HANDLERS_HT_BITS 8
 static DEFINE_HASHTABLE(prop_handlers_ht, BTRFS_PROP_HANDLERS_HT_BITS);
 
@@ -27,7 +36,7 @@ struct prop_handler {
 	int (*validate)(const struct btrfs_inode *inode, const char *value,
 			size_t len);
 	int (*apply)(struct btrfs_inode *inode, const char *value, size_t len);
-	const char *(*extract)(const struct btrfs_inode *inode);
+	const char *(*extract)(const struct btrfs_inode *inode, char *buf, size_t len);
 	bool (*ignore)(const struct btrfs_inode *inode);
 	int inheritable;
 };
@@ -395,12 +404,19 @@ static bool prop_compression_ignore(const struct btrfs_inode *inode)
 	return false;
 }
 
-static const char *prop_compression_extract(const struct btrfs_inode *inode)
+static const char *prop_compression_extract(const struct btrfs_inode *inode,
+					    char *buf, size_t len)
 {
 	switch (inode->prop_compress) {
 	case BTRFS_COMPRESS_ZLIB:
 	case BTRFS_COMPRESS_LZO:
 	case BTRFS_COMPRESS_ZSTD:
+		if (inode->prop_compress_level) {
+			snprintf(buf, len, "%s:%d",
+				 btrfs_compress_type2str(inode->prop_compress),
+				 inode->prop_compress_level);
+			return buf;
+		}
 		return btrfs_compress_type2str(inode->prop_compress);
 	default:
 		break;
@@ -437,6 +453,7 @@ int btrfs_inode_inherit_props(struct btrfs_trans_handle *trans,
 		const struct prop_handler *h = &prop_handlers[i];
 		const char *value;
 		u64 num_bytes = 0;
+		char buf[BTRFS_COMPRESS_PROP_MAX_LEN];
 
 		if (!h->inheritable)
 			continue;
@@ -444,7 +461,7 @@ int btrfs_inode_inherit_props(struct btrfs_trans_handle *trans,
 		if (h->ignore(inode))
 			continue;
 
-		value = h->extract(parent);
+		value = h->extract(parent, buf, sizeof(buf));
 		if (!value)
 			continue;
 
-- 
2.55.0