History:
During the discussion over the speed and stability of the proposed inclusion
of a stripped-down, minimized version of the LZO compression algorithm it was
noted that the way that patch handled separation of compression and
decompression could be used for zlib as well. Then it was noted that moving
the private zlib header 'zutil.h' to a combined zlib directory would break
JFFS2, which used it. On examining JFFS2 it became clear that the only thing
JFFS2 used the header for was a single constant. Since his code was involved,
Mark Adler was contacted and he stated that that constant - PRESET_DICT - was
part of the zlib standard and defined in RFC 1950. So, to remove the
dependency the simplest recourse is to replace PRESET_DICT with the 'magic
number' it represents.
Signed-off-by: Daniel Hazelton <[email protected]>
DRH
diff --git a/fs/jffs2/compr_zlib.c b/fs/jffs2/compr_zlib.c
index 2b87fcc..9f1b935 100644
--- a/fs/jffs2/compr_zlib.c
+++ b/fs/jffs2/compr_zlib.c
@@ -16,7 +16,6 @@
#include <linux/kernel.h>
#include <linux/slab.h>
#include <linux/zlib.h>
-#include <linux/zutil.h>
#include "nodelist.h"
#include "compr.h"
@@ -154,7 +153,7 @@ static int jffs2_zlib_decompress(unsigned char *data_in,
/* If it's deflate, and it's got no preset dictionary, then
we can tell zlib to skip the adler32 check. */
- if (srclen > 2 && !(data_in[1] & PRESET_DICT) &&
+ if (srclen > 2 && !(data_in[1] & 0x20) &&
((data_in[0] & 0x0f) == Z_DEFLATED) &&
!(((data_in[0]<<8) + data_in[1]) % 31)) {
Daniel Hazelton wrote:
>
> Signed-off-by: Daniel Hazelton <[email protected]>
>
> DRH
>
> diff --git a/fs/jffs2/compr_zlib.c b/fs/jffs2/compr_zlib.c
> index 2b87fcc..9f1b935 100644
> --- a/fs/jffs2/compr_zlib.c
> +++ b/fs/jffs2/compr_zlib.c
> @@ -16,7 +16,6 @@
> #include <linux/kernel.h>
> #include <linux/slab.h>
> #include <linux/zlib.h>
> -#include <linux/zutil.h>
> #include "nodelist.h"
> #include "compr.h"
>
> @@ -154,7 +153,7 @@ static int jffs2_zlib_decompress(unsigned char *data_in,
>
> /* If it's deflate, and it's got no preset dictionary, then
> we can tell zlib to skip the adler32 check. */
> - if (srclen > 2 && !(data_in[1] & PRESET_DICT) &&
> + if (srclen > 2 && !(data_in[1] & 0x20) &&
> ((data_in[0] & 0x0f) == Z_DEFLATED) &&
> !(((data_in[0]<<8) + data_in[1]) % 31)) {
>
Why not
#define PRESET_DICT 0x20
instead of obfuscating the code with a magic number ? (Or name it
differently if it clashes with something else...)
Cheers,
Prakash
On Saturday 02 June 2007 20:21:13 Prakash Punnoor wrote:
> Daniel Hazelton wrote:
> > Signed-off-by: Daniel Hazelton <[email protected]>
> >
> > DRH
> >
> > diff --git a/fs/jffs2/compr_zlib.c b/fs/jffs2/compr_zlib.c
> > index 2b87fcc..9f1b935 100644
> > --- a/fs/jffs2/compr_zlib.c
> > +++ b/fs/jffs2/compr_zlib.c
> > @@ -16,7 +16,6 @@
> > #include <linux/kernel.h>
> > #include <linux/slab.h>
> > #include <linux/zlib.h>
> > -#include <linux/zutil.h>
> > #include "nodelist.h"
> > #include "compr.h"
> >
> > @@ -154,7 +153,7 @@ static int jffs2_zlib_decompress(unsigned char
> > *data_in,
> >
> > /* If it's deflate, and it's got no preset dictionary, then
> > we can tell zlib to skip the adler32 check. */
> > - if (srclen > 2 && !(data_in[1] & PRESET_DICT) &&
> > + if (srclen > 2 && !(data_in[1] & 0x20) &&
> > ((data_in[0] & 0x0f) == Z_DEFLATED) &&
> > !(((data_in[0]<<8) + data_in[1]) % 31)) {
>
> Why not
>
> #define PRESET_DICT 0x20
>
> instead of obfuscating the code with a magic number ? (Or name it
> differently if it clashes with something else...)
>
>
> Cheers,
>
> Prakash
Not a problem. This patch was just a result of a quick s/PRESET_DICT/0x20/p -
I'll change the patch so there is a localized PRESET_DICT macro.
I've attached an updated patch that does just that.
(Mark Adler suggested a second, more involved patch that would put the burdon
of all the checking that JFFS2 is doing where it belongs, and already is done
actually, zlib's inflate() )
DRH
diff --git a/fs/jffs2/compr_zlib.c b/fs/jffs2/compr_zlib.c
index 2b87fcc..f4519db 100644
--- a/fs/jffs2/compr_zlib.c
+++ b/fs/jffs2/compr_zlib.c
@@ -16,7 +16,6 @@
#include <linux/kernel.h>
#include <linux/slab.h>
#include <linux/zlib.h>
-#include <linux/zutil.h>
#include "nodelist.h"
#include "compr.h"
@@ -29,6 +28,13 @@
*/
#define STREAM_END_SPACE 12
+/*
+ * PRESET_DICT is set in the internal (aka: private) zlib header zutil.h
+ * the value - 0x20 - is defined in RFC 1950, so making a duplicate
+ * definition here to remove this code's dependency on that file is safe.
+ */
+#define PRESET_DICT 0x20
+
static DEFINE_MUTEX(deflate_mutex);
static DEFINE_MUTEX(inflate_mutex);
static z_stream inf_strm, def_strm;
No code besides zlib itself should depend on linux/zutil.h - the only item
JFFS2 uses from that header is a constant that is defined in RFC 1950 and
should never change. This patch mirrors the #define in zutil.h and removes
the #include.
Signed-off-by: Daniel Hazelton <[email protected]>
DRH
diff --git a/fs/jffs2/compr_zlib.c b/fs/jffs2/compr_zlib.c
index 2b87fcc..f4519db 100644
--- a/fs/jffs2/compr_zlib.c
+++ b/fs/jffs2/compr_zlib.c
@@ -16,7 +16,6 @@
#include <linux/kernel.h>
#include <linux/slab.h>
#include <linux/zlib.h>
-#include <linux/zutil.h>
#include "nodelist.h"
#include "compr.h"
@@ -29,6 +28,13 @@
*/
#define STREAM_END_SPACE 12
+/*
+ * PRESET_DICT is set in the internal (aka: private) zlib header zutil.h
+ * the value - 0x20 - is defined in RFC 1950, so making a duplicate
+ * definition here to remove this code's dependency on that file is safe.
+ */
+#define PRESET_DICT 0x20
+
static DEFINE_MUTEX(deflate_mutex);
static DEFINE_MUTEX(inflate_mutex);
static z_stream inf_strm, def_strm;