jffs2: allow disabling of compression schemes at runtime

PATCH In review Andres Salomon 2 participants 4 messages Oct 4, 2011 – Oct 14, 2011

Subsystems (2)

Memory technology devices (MTD) Journalling flash file system V2 (JFFS2)

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Andres Salomon

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2011-10-04 02:16 UTC #0 lore raw

PATCH 1/1 jffs2: allow disabling of compression schemes at runtime

Currently jffs2 has compile-time constants (and .config options) regarding whether or not the various compression/decompression drivers are built in and enabled. This is fine for embedded systems, but it clashes with distribution kernels. Distro kernels tend to turn on everything; this causes OpenFirmware to fall over, as it only supports ZLIB decompression. Booting a kernel that has LZO compression enabled, writing to the boot partition, and then rebooting causes OFW to fail to read the kernel from the filesystem. This is because LZO compression has priority when writing new data to jffs2, if LZO is enabled.

To get around that, this patch adds jffs2 module params for each compressor type that isn't decompression-only. That means I can run a kernel that has support for LZO and ZLIB decompression (allowing me to read LZO data off of the root partition), while disabling LZO compression writes (jffs2.disable_lzo=1) so that the boot partition stays compatible with OFW.

Signed-off-by Andres Salomon <[email protected]>

---
 fs/jffs2/compr_lzo.c   |    4 ++++
 fs/jffs2/compr_rtime.c |    7 +++++++
 fs/jffs2/compr_rubin.c |   11 +++++++++++
 fs/jffs2/compr_zlib.c  |    6 ++++++
 4 files changed, 28 insertions(+), 0 deletions(-)

fs/jffs2/compr_lzo.c +4 -0

index af186ee..4a1ab10 100644
@@ -14,6 +14,7 @@
 #include <linux/sched.h>
 #include <linux/vmalloc.h>
 #include <linux/init.h>
+#include <linux/module.h>
 #include <linux/lzo.h>
 #include "compr.h"

@@ -89,6 +90,9 @@ static struct jffs2_compressor jffs2_lzo_comp = {
 	.disabled = 0,
 };
 
+module_param_named(disable_lzo, jffs2_lzo_comp.disabled, int, 0);
+MODULE_PARM_DESC(disable_lzo, "Disable lzo compression.  Default: 0.");
+
 int __init jffs2_lzo_init(void)
 {
 	int ret;

fs/jffs2/compr_rtime.c +7 -0

index 16a5047..0c0725b 100644
@@ -24,6 +24,7 @@
 #include <linux/kernel.h>
 #include <linux/types.h>
 #include <linux/errno.h>
+#include <linux/module.h>
 #include <linux/string.h>
 #include <linux/jffs2.h>
 #include "compr.h"

@@ -119,6 +120,12 @@ static struct jffs2_compressor jffs2_rtime_comp = {
 #endif
 };
 
+#ifndef JFFS2_RTIME_DISABLED
+module_param_named(disable_rtime, jffs2_rtime_comp.disabled, int, 0);
+MODULE_PARM_DESC(disable_rtime, "Disable rtime compression.  Default: 0.");
+#endif
+
+
 int jffs2_rtime_init(void)
 {
     return jffs2_register_compressor(&jffs2_rtime_comp);

fs/jffs2/compr_rubin.c +11 -0

index 9e7cec8..8fd570a 100644
@@ -12,6 +12,7 @@
 
 #include <linux/string.h>
 #include <linux/types.h>
+#include <linux/module.h>
 #include <linux/jffs2.h>
 #include <linux/errno.h>
 #include "compr.h"

@@ -421,6 +422,11 @@ static struct jffs2_compressor jffs2_rubinmips_comp = {
 #endif
 };
 
+#ifndef JFFS2_RUBINMIPS_DISABLED
+module_param_named(disable_rubinmips, jffs2_rubinmips_comp.disabled, int, 0);
+MODULE_PARM_DESC(disable_rubinmips, "Disable rubinmips compression.  Default: 0.");
+#endif
+
 int jffs2_rubinmips_init(void)
 {
 	return jffs2_register_compressor(&jffs2_rubinmips_comp);

@@ -444,6 +450,11 @@ static struct jffs2_compressor jffs2_dynrubin_comp = {
 #endif
 };
 
+#ifndef JFFS2_DYNRUBIN_DISABLED
+module_param_named(disable_dynrubin, jffs2_dynrubin_comp.disabled, int, 0);
+MODULE_PARM_DESC(disable_dynrubin, "Disable dynrubin compression.  Default: 0.");
+#endif
+
 int jffs2_dynrubin_init(void)
 {
 	return jffs2_register_compressor(&jffs2_dynrubin_comp);

fs/jffs2/compr_zlib.c +6 -0

index 5a00102..9cd1896 100644
@@ -37,6 +37,7 @@ static z_stream inf_strm, def_strm;
 #include <linux/vmalloc.h>
 #include <linux/init.h>
 #include <linux/mutex.h>
+#include <linux/module.h>
 
 static int __init alloc_workspaces(void)
 {

@@ -196,6 +197,11 @@ static struct jffs2_compressor jffs2_zlib_comp = {
 #endif
 };
 
+#ifndef JFFS2_ZLIB_DISABLED
+module_param_named(disable_zlib, jffs2_zlib_comp.disabled, int, 0);
+MODULE_PARM_DESC(disable_zlib, "Disable zlib compression.  Default: 0.");
+#endif
+
 int __init jffs2_zlib_init(void)
 {
     int ret;

Signature · 1 line

1.7.2.5

Artem Bityutskiy

2011-10-14 08:51 UTC #1 lore raw

Quoted 11 lines · Andres Salomon

Currently jffs2 has compile-time constants (and .config options) regarding whether or not the various compression/decompression drivers are built in and enabled. This is fine for embedded systems, but it clashes with distribution kernels. Distro kernels tend to turn on everything; this causes OpenFirmware to fall over, as it only supports ZLIB decompression. Booting a kernel that has LZO compression enabled, writing to the boot partition, and then rebooting causes OFW to fail to read the kernel from the filesystem. This is because LZO compression has priority when writing new data to jffs2, if LZO is enabled.

Quoted 8 lines

To get around that, this patch adds jffs2 module params for each compressor type that isn't decompression-only. That means I can run a kernel that has support for LZO and ZLIB decompression (allowing me to read LZO data off of the root partition), while disabling LZO compression writes (jffs2.disable_lzo=1) so that the boot partition stays compatible with OFW.
Signed-off-by Andres Salomon <[email protected]>

You should use mount options instead. Invent nice mount options to configure compression strategy of JFFS2.

Or you can simply implement the same option as UBIFS has: compr=xxx.

See Documentation/filesystems/ubifs.txt

With this option you set the default compressor which is use when writing, and on reading all decompression are supported, seems like exactly what you want. You can also look how it is implemented in UBIFS for reference.

Signature · 2 lines

Best Regards,
Artem Bityutskiy

Andres Salomon

author

2011-10-14 14:14 UTC #2 lore raw

Quoted 19 lines · On Fri, 14 Oct 2011 11:50:37 +0300 Artem Bityutskiy <[email protected]> wrote:

Quoted 18 lines · Andres Salomon
Currently jffs2 has compile-time constants (and .config options) regarding whether or not the various compression/decompression drivers are built in and enabled. This is fine for embedded systems, but it clashes with distribution kernels. Distro kernels tend to turn on everything; this causes OpenFirmware to fall over, as it only supports ZLIB decompression. Booting a kernel that has LZO compression enabled, writing to the boot partition, and then rebooting causes OFW to fail to read the kernel from the filesystem. This is because LZO compression has priority when writing new data to jffs2, if LZO is enabled.
To get around that, this patch adds jffs2 module params for each compressor type that isn't decompression-only. That means I can run a kernel that has support for LZO and ZLIB decompression (allowing me to read LZO data off of the root partition), while disabling LZO compression writes (jffs2.disable_lzo=1) so that the boot partition stays compatible with OFW.

Quoted 4 lines

Quoted 1 line
Signed-off-by Andres Salomon <[email protected]>
You should use mount options instead. Invent nice mount options to configure compression strategy of JFFS2.

I thought about it, but currently jffs2 doesn't support parsing mount options. It seemed like a lot of extra code for such an obscure feature, on a filesystem that's merely in maintenance mode (I don't know if anyone else has run into the same issue that I have). However, I can do that if desired.

Quoted 3 lines

Or you can simply implement the same option as UBIFS has: compr=xxx.

Yep.

Quoted 7 lines

See Documentation/filesystems/ubifs.txt
With this option you set the default compressor which is use when writing, and on reading all decompression are supported, seems like exactly what you want. You can also look how it is implemented in UBIFS for reference.

Artem Bityutskiy

2011-10-14 14:23 UTC #3 lore raw

Quoted 24 lines · Andres Salomon

Quoted 21 lines · On Fri, 14 Oct 2011 11:50:37 +0300 Artem Bityutskiy <[email protected]> wrote:
Quoted 19 lines · Andres Salomon
Currently jffs2 has compile-time constants (and .config options) regarding whether or not the various compression/decompression drivers are built in and enabled. This is fine for embedded systems, but it clashes with distribution kernels. Distro kernels tend to turn on everything; this causes OpenFirmware to fall over, as it only supports ZLIB decompression. Booting a kernel that has LZO compression enabled, writing to the boot partition, and then rebooting causes OFW to fail to read the kernel from the filesystem. This is because LZO compression has priority when writing new data to jffs2, if LZO is enabled.
To get around that, this patch adds jffs2 module params for each compressor type that isn't decompression-only. That means I can run a kernel that has support for LZO and ZLIB decompression (allowing me to read LZO data off of the root partition), while disabling LZO compression writes (jffs2.disable_lzo=1) so that the boot partition stays compatible with OFW.
Signed-off-by Andres Salomon <[email protected]>

Quoted 8 lines

Quoted 2 lines
You should use mount options instead. Invent nice mount options to configure compression strategy of JFFS2.
I thought about it, but currently jffs2 doesn't support parsing mount options. It seemed like a lot of extra code for such an obscure feature, on a filesystem that's merely in maintenance mode (I don't know if anyone else has run into the same issue that I have). However, I can do that if desired.

Yeah, but module parameter for FS is very unusual thing. It should not be very difficult to introduce an option, really. Mount and remount just give you the string where you can find every non-standard mount option. And you can copypaste parts UBIFS code and tweak it.

Signature · 2 lines

Best Regards,
Artem Bityutskiy