[Buildroot] [PATCH 0/2] Creating a sparse file in ROOTFS_F2FS_CMD

[Buildroot] [PATCH 0/2] Creating a sparse file in ROOTFS_F2FS_CMD

[Grzegorz Blach]

I'm not sure if creating a sparse file using `dd` command from host OS
is acceptable.  Maybe it's needed to find a better solution.

Grzegorz Blach (2):
  package/f2fs-tools: add host package
  fs/f2fs: add support for creating a f2fs image

 DEVELOPERS                        |  1 +
 fs/Config.in                      |  1 +
 fs/f2fs/Config.in                 | 49 +++++++++++++++++++++++++++++++
 fs/f2fs/f2fs.mk                   | 46 +++++++++++++++++++++++++++++
 package/Config.in.host            |  1 +
 package/f2fs-tools/Config.in.host |  7 +++++
 package/f2fs-tools/f2fs-tools.mk  |  2 ++
 7 files changed, 107 insertions(+)
 create mode 100644 fs/f2fs/Config.in
 create mode 100644 fs/f2fs/f2fs.mk
 create mode 100644 package/f2fs-tools/Config.in.host

-- 
2.17.2

[Buildroot] [PATCH 1/2] package/f2fs-tools: add host package

[Grzegorz Blach]

This package is useful to create f2fs filesystem during build process.

Signed-off-by: Grzegorz Blach <grzegorz@blach.pl>
---
 DEVELOPERS                        | 1 +
 package/Config.in.host            | 1 +
 package/f2fs-tools/Config.in.host | 7 +++++++
 package/f2fs-tools/f2fs-tools.mk  | 2 ++
 4 files changed, 11 insertions(+)
 create mode 100644 package/f2fs-tools/Config.in.host

diff --git a/DEVELOPERS b/DEVELOPERS
index a3d97eb390..6b708c69c4 100644
--- a/DEVELOPERS
+++ b/DEVELOPERS
@@ -891,6 +891,7 @@ F:	package/sofia-sip/
 
 N:	Grzegorz Blach <grzegorz@blach.pl>
 F:	package/bluez5_utils-headers/
+F:	package/f2fs-tools/
 F:	package/pigpio/
 F:	package/python-falcon/
 F:	package/python-mimeparse/
diff --git a/package/Config.in.host b/package/Config.in.host
index 3a3578ceeb..16b474fc9d 100644
--- a/package/Config.in.host
+++ b/package/Config.in.host
@@ -16,6 +16,7 @@ menu "Host utilities"
 	source "package/dtc/Config.in.host"
 	source "package/e2fsprogs/Config.in.host"
 	source "package/e2tools/Config.in.host"
+	source "package/f2fs-tools/Config.in.host"
 	source "package/faketime/Config.in.host"
 	source "package/fwup/Config.in.host"
 	source "package/genext2fs/Config.in.host"
diff --git a/package/f2fs-tools/Config.in.host b/package/f2fs-tools/Config.in.host
new file mode 100644
index 0000000000..19c77b9c89
--- /dev/null
+++ b/package/f2fs-tools/Config.in.host
@@ -0,0 +1,7 @@
+config BR2_PACKAGE_HOST_F2FS_TOOLS
+	bool "host f2fs-tools"
+	select BR2_PACKAGE_HOST_UTIL_LINUX
+	help
+	  Tools for Flash-Friendly File System (F2FS)
+
+	  https://git.kernel.org/pub/scm/linux/kernel/git/jaegeuk/f2fs-tools.git
diff --git a/package/f2fs-tools/f2fs-tools.mk b/package/f2fs-tools/f2fs-tools.mk
index 119cef35cc..7973ebf570 100644
--- a/package/f2fs-tools/f2fs-tools.mk
+++ b/package/f2fs-tools/f2fs-tools.mk
@@ -9,6 +9,7 @@ F2FS_TOOLS_SITE = http://git.kernel.org/pub/scm/linux/kernel/git/jaegeuk/f2fs-to
 F2FS_TOOLS_SITE_METHOD = git
 F2FS_TOOLS_CONF_ENV = ac_cv_file__git=no
 F2FS_TOOLS_DEPENDENCIES = host-pkgconf util-linux
+HOST_F2FS_TOOLS_DEPENDENCIES = host-pkgconf host-util-linux
 # GIT version, shipped without configure
 F2FS_TOOLS_AUTORECONF = YES
 F2FS_TOOLS_INSTALL_STAGING = YES
@@ -30,3 +31,4 @@ F2FS_TOOLS_CONF_OPTS += --without-blkid
 endif
 
 $(eval $(autotools-package))
+$(eval $(host-autotools-package))
-- 
2.17.2

[Buildroot] [PATCH 2/2] fs/f2fs: add support for creating a f2fs image

[Grzegorz Blach]

This patch makes possible to create rootfs image using f2fs filesystem.

Signed-off-by: Grzegorz Blach <grzegorz@blach.pl>
---
 fs/Config.in      |  1 +
 fs/f2fs/Config.in | 49 +++++++++++++++++++++++++++++++++++++++++++++++
 fs/f2fs/f2fs.mk   | 46 ++++++++++++++++++++++++++++++++++++++++++++
 3 files changed, 96 insertions(+)
 create mode 100644 fs/f2fs/Config.in
 create mode 100644 fs/f2fs/f2fs.mk

diff --git a/fs/Config.in b/fs/Config.in
index 24f22fd7e3..527051ef54 100644
--- a/fs/Config.in
+++ b/fs/Config.in
@@ -6,6 +6,7 @@ source "fs/cloop/Config.in"
 source "fs/cpio/Config.in"
 source "fs/cramfs/Config.in"
 source "fs/ext2/Config.in"
+source "fs/f2fs/Config.in"
 source "fs/initramfs/Config.in"
 source "fs/iso9660/Config.in"
 source "fs/jffs2/Config.in"
diff --git a/fs/f2fs/Config.in b/fs/f2fs/Config.in
new file mode 100644
index 0000000000..d096057890
--- /dev/null
+++ b/fs/f2fs/Config.in
@@ -0,0 +1,49 @@
+config BR2_TARGET_ROOTFS_F2FS
+	bool "f2fs root filesystem"
+	select BR2_PACKAGE_HOST_F2FS_TOOLS
+	help
+	  Build a f2fs root filesystem. If you enable this option, you
+	  probably want to enable the f2fs-tools package too.
+
+if BR2_TARGET_ROOTFS_F2FS
+
+config BR2_TARGET_ROOTFS_F2FS_LABEL
+	string "filesystem label"
+
+config BR2_TARGET_ROOTFS_F2FS_SIZE
+	string "filesystem size"
+	default "100M"
+	help
+	  The size of the filesystem image in bytes.
+	  Suffix with K, M, G or T for power-of-two kilo-, mega-, giga-
+	  or terabytes.
+
+config BR2_TARGET_ROOTFS_F2FS_COLD_FILES
+	string "extension list for cold files"
+	help
+	  Specify a file extension list in order f2fs to treat them
+	  as cold files. The default list includes most of multimedia
+	  file extensions such as jpg, gif, mpeg, mkv, and so on.
+
+config BR2_TARGET_ROOTFS_F2FS_OVERPROVISION
+	int "size for overprovision area (0 for auto calculation)"
+	default 0
+	help
+	  Specify the percentage over the volume size for overprovision
+	  area. This area is hidden to users, and utilized by F2FS
+	  cleaner. If not specified, the best number will be assigned
+	  automatically accoring to the partition size.
+
+config BR2_TARGET_ROOTFS_F2FS_FEATURES
+	string "filesystem features"
+	help
+	  A feature list in order f2fs filesystem will supports.
+	  e.g "encrypt" and so on.
+
+config BR2_TARGET_ROOTFS_F2FS_DISCARD
+	bool "discard policy"
+	default y
+	help
+	  Enable or disable discard policy.
+
+endif # BR2_TARGET_ROOTFS_F2FS
diff --git a/fs/f2fs/f2fs.mk b/fs/f2fs/f2fs.mk
new file mode 100644
index 0000000000..19c0082d67
--- /dev/null
+++ b/fs/f2fs/f2fs.mk
@@ -0,0 +1,46 @@
+################################################################################
+#
+# Build the f2fs root filesystem image
+#
+################################################################################
+
+F2FS_SIZE = $(call qstrip,$(BR2_TARGET_ROOTFS_F2FS_SIZE))
+ifeq ($(BR2_TARGET_ROOTFS_F2FS)-$(F2FS_SIZE),y-)
+$(error BR2_TARGET_ROOTFS_F2FS_SIZE cannot be empty)
+endif
+
+F2FS_COLD_FILES = $(call qstrip,$(BR2_TARGET_ROOTFS_F2FS_COLD_FILES))
+F2FS_FEATURES = $(call qstrip,$(BR2_TARGET_ROOTFS_F2FS_FEATURES))
+# qstrip results in stripping consecutive spaces into a single one. So the
+# variable is not qstrip-ed to preserve the integrity of the string value.
+F2FS_LABEL := $(subst ",,$(BR2_TARGET_ROOTFS_F2FS_LABEL))
+# ")
+
+ifneq ($(BR2_TARGET_ROOTFS_F2FS_OVERPROVISION),0)
+F2FS_OVERPROVISION=$(BR2_TARGET_ROOTFS_F2FS_OVERPROVISION)
+endif
+
+ifeq ($(BR2_TARGET_ROOTFS_F2FS_DISCARD),y)
+F2FS_DISCARD=1
+else
+F2FS_DISCARD=0
+endif
+
+F2FS_OPTS = \
+	-f \
+	-l "$(F2FS_LABEL)" \
+	$(if $(F2FS_COLD_FILES),-e "$(F2FS_COLD_FILES)") \
+	$(if $(F2FS_OVERPROVISION),-o $(F2FS_OVERPROVISION)) \
+	$(if $(F2FS_FEATURES),-O "$(F2FS_FEATURES)") \
+	-t $(F2FS_DISCARD)
+
+ROOTFS_F2FS_DEPENDENCIES = host-f2fs-tools
+
+define ROOTFS_F2FS_CMD
+	$(RM) -f $@
+	dd if=/dev/zero of=$@ bs=1 count=0 seek=$(F2FS_SIZE)
+	$(HOST_DIR)/sbin/mkfs.f2fs $(F2FS_OPTS) $@
+	$(HOST_DIR)/sbin/sload.f2fs -f $(TARGET_DIR) $@
+endef
+
+$(eval $(rootfs))
-- 
2.17.2

[Buildroot] [PATCH 1/2] package/f2fs-tools: add host package

[Yann E. MORIN]

Grzegorz, All,

On 2018-10-26 22:00 +0200, Grzegorz Blach spake thusly:
> This package is useful to create f2fs filesystem during build process.

Indeed.

> Signed-off-by: Grzegorz Blach <grzegorz@blach.pl>
> ---
[--SNIP--]
> diff --git a/package/f2fs-tools/f2fs-tools.mk b/package/f2fs-tools/f2fs-tools.mk
> index 119cef35cc..7973ebf570 100644
> --- a/package/f2fs-tools/f2fs-tools.mk
> +++ b/package/f2fs-tools/f2fs-tools.mk
> @@ -9,6 +9,7 @@ F2FS_TOOLS_SITE = http://git.kernel.org/pub/scm/linux/kernel/git/jaegeuk/f2fs-to
>  F2FS_TOOLS_SITE_METHOD = git
>  F2FS_TOOLS_CONF_ENV = ac_cv_file__git=no
>  F2FS_TOOLS_DEPENDENCIES = host-pkgconf util-linux
> +HOST_F2FS_TOOLS_DEPENDENCIES = host-pkgconf host-util-linux
>  # GIT version, shipped without configure
>  F2FS_TOOLS_AUTORECONF = YES
>  F2FS_TOOLS_INSTALL_STAGING = YES
> @@ -30,3 +31,4 @@ F2FS_TOOLS_CONF_OPTS += --without-blkid
>  endif

I don't think that libblkid is needed for the host variant, so we should
probably explicitly disable it. On the other hand, libblkid is always
built by host-util-linux.

Whatever yuou choose, make that explicit.

Also, we do have host-libselinux, so wyou may want to also enable that
unconditionally.

    HOST_F2FS_TOOLS_DEPENDENCIES = \
        host-libselinux \
        host-pkgconf \
        host-util-linux

    HOST_F2FS_TOOLS_CONF_OPTS = --without-blkid --with-selinux

Regards,
Yann E. MORIN.

>  $(eval $(autotools-package))
> +$(eval $(host-autotools-package))
> -- 
> 2.17.2
> 
> _______________________________________________
> buildroot mailing list
> buildroot at busybox.net
> http://lists.busybox.net/mailman/listinfo/buildroot

-- 
.-----------------.--------------------.------------------.--------------------.
|  Yann E. MORIN  | Real-Time Embedded | /"\ ASCII RIBBON | Erics' conspiracy: |
| +33 662 376 056 | Software  Designer | \ / CAMPAIGN     |  ___               |
| +33 223 225 172 `------------.-------:  X  AGAINST      |  \e/  There is no  |
| http://ymorin.is-a-geek.org/ | _/*\_ | / \ HTML MAIL    |   v   conspiracy.  |
'------------------------------^-------^------------------^--------------------'

[Buildroot] [PATCH 2/2] fs/f2fs: add support for creating a f2fs image

[Yann E. MORIN]

Grzegorz, All,

On 2018-10-26 22:00 +0200, Grzegorz Blach spake thusly:
> This patch makes possible to create rootfs image using f2fs filesystem.
> 
> Signed-off-by: Grzegorz Blach <grzegorz@blach.pl>
> ---
[--SNIP--]
> diff --git a/fs/f2fs/Config.in b/fs/f2fs/Config.in
> new file mode 100644
> index 0000000000..d096057890
> --- /dev/null
> +++ b/fs/f2fs/Config.in
> @@ -0,0 +1,49 @@
> +config BR2_TARGET_ROOTFS_F2FS
> +	bool "f2fs root filesystem"
> +	select BR2_PACKAGE_HOST_F2FS_TOOLS
> +	help
> +	  Build a f2fs root filesystem. If you enable this option, you
> +	  probably want to enable the f2fs-tools package too.
> +
> +if BR2_TARGET_ROOTFS_F2FS
> +
> +config BR2_TARGET_ROOTFS_F2FS_LABEL
> +	string "filesystem label"
> +
> +config BR2_TARGET_ROOTFS_F2FS_SIZE
> +	string "filesystem size"
> +	default "100M"
> +	help
> +	  The size of the filesystem image in bytes.
> +	  Suffix with K, M, G or T for power-of-two kilo-, mega-, giga-
> +	  or terabytes.
> +
> +config BR2_TARGET_ROOTFS_F2FS_COLD_FILES
> +	string "extension list for cold files"
> +	help
> +	  Specify a file extension list in order f2fs to treat them
> +	  as cold files. The default list includes most of multimedia
> +	  file extensions such as jpg, gif, mpeg, mkv, and so on.

I would prefer that we get a first patch that adds the bare minimal
needed to assemble an f2fs image, with further patches adding more
features one by one, as it is easier to review.

This "cold files" feature should be added in its own patch.

> +config BR2_TARGET_ROOTFS_F2FS_OVERPROVISION
> +	int "size for overprovision area (0 for auto calculation)"
> +	default 0
> +	help
> +	  Specify the percentage over the volume size for overprovision
> +	  area. This area is hidden to users, and utilized by F2FS
> +	  cleaner. If not specified, the best number will be assigned
> +	  automatically accoring to the partition size.

May I suggest an alternative wording?

    int "size for overprovision area"
    default 0
    help
      The percentage over the volume size for overprovision area. This
      area is hidden to users, and utilized by F2FS cleaner.

      Leave at 0 for autocalculation.

But this feature should be added in its own patch.

> +config BR2_TARGET_ROOTFS_F2FS_FEATURES
> +	string "filesystem features"
> +	help
> +	  A feature list in order f2fs filesystem will supports.
> +	  e.g "encrypt" and so on.

Ditto, a separate patch. Also, this option being a plain string, I'd
prefer it goes last in the list of options, below the discard one.

> +config BR2_TARGET_ROOTFS_F2FS_DISCARD
> +	bool "discard policy"
> +	default y
> +	help
> +	  Enable or disable discard policy.

Ditto, a separate patch for that one, please.

> +endif # BR2_TARGET_ROOTFS_F2FS
> diff --git a/fs/f2fs/f2fs.mk b/fs/f2fs/f2fs.mk
> new file mode 100644
> index 0000000000..19c0082d67
> --- /dev/null
> +++ b/fs/f2fs/f2fs.mk
> @@ -0,0 +1,46 @@
> +################################################################################
> +#
> +# Build the f2fs root filesystem image
> +#
> +################################################################################
> +
> +F2FS_SIZE = $(call qstrip,$(BR2_TARGET_ROOTFS_F2FS_SIZE))
> +ifeq ($(BR2_TARGET_ROOTFS_F2FS)-$(F2FS_SIZE),y-)
> +$(error BR2_TARGET_ROOTFS_F2FS_SIZE cannot be empty)
> +endif
> +
> +F2FS_COLD_FILES = $(call qstrip,$(BR2_TARGET_ROOTFS_F2FS_COLD_FILES))
> +F2FS_FEATURES = $(call qstrip,$(BR2_TARGET_ROOTFS_F2FS_FEATURES))
> +# qstrip results in stripping consecutive spaces into a single one. So the
> +# variable is not qstrip-ed to preserve the integrity of the string value.
> +F2FS_LABEL := $(subst ",,$(BR2_TARGET_ROOTFS_F2FS_LABEL))
> +# ")
> +
> +ifneq ($(BR2_TARGET_ROOTFS_F2FS_OVERPROVISION),0)
> +F2FS_OVERPROVISION=$(BR2_TARGET_ROOTFS_F2FS_OVERPROVISION)
> +endif
> +
> +ifeq ($(BR2_TARGET_ROOTFS_F2FS_DISCARD),y)
> +F2FS_DISCARD=1
> +else
> +F2FS_DISCARD=0
> +endif
> +
> +F2FS_OPTS = \
> +	-f \
> +	-l "$(F2FS_LABEL)" \
> +	$(if $(F2FS_COLD_FILES),-e "$(F2FS_COLD_FILES)") \
> +	$(if $(F2FS_OVERPROVISION),-o $(F2FS_OVERPROVISION)) \
> +	$(if $(F2FS_FEATURES),-O "$(F2FS_FEATURES)") \
> +	-t $(F2FS_DISCARD)

Conditional values should go last:

    F2FS_OPTS = \
        -f \
        -l "$(F2FS_LABEL)" \
        -t $(F2FS_DISCARD) \
        $(if $(F2FS_COLD_FILES),-e "$(F2FS_COLD_FILES)") \
        [...]

> +ROOTFS_F2FS_DEPENDENCIES = host-f2fs-tools
> +
> +define ROOTFS_F2FS_CMD
> +	$(RM) -f $@
> +	dd if=/dev/zero of=$@ bs=1 count=0 seek=$(F2FS_SIZE)

You mentionned in your cover letter that you were not sure using dd was
the best solution. It is acceptable, but usng truncate might be a better
option, and you can alsoirectly pass it the size value:

    truncate -s '$(F2FS_SIZE)' $@

Otherwise, when using dd to achieve the same, I invert bs and seek:
(i.e. it is 1 bloc of N, not N blocs of 1).

    dd if=/dev/zero of=$@ bs=$(F2FS_SIZE) count=0 seek=1

So, dd is acceptable, but I'd favour truncate.

Regards,
Yann E. MORIN.

> +	$(HOST_DIR)/sbin/mkfs.f2fs $(F2FS_OPTS) $@
> +	$(HOST_DIR)/sbin/sload.f2fs -f $(TARGET_DIR) $@
> +endef
> +
> +$(eval $(rootfs))
> -- 
> 2.17.2
> 
> _______________________________________________
> buildroot mailing list
> buildroot at busybox.net
> http://lists.busybox.net/mailman/listinfo/buildroot

-- 
.-----------------.--------------------.------------------.--------------------.
|  Yann E. MORIN  | Real-Time Embedded | /"\ ASCII RIBBON | Erics' conspiracy: |
| +33 662 376 056 | Software  Designer | \ / CAMPAIGN     |  ___               |
| +33 223 225 172 `------------.-------:  X  AGAINST      |  \e/  There is no  |
| http://ymorin.is-a-geek.org/ | _/*\_ | / \ HTML MAIL    |   v   conspiracy.  |
'------------------------------^-------^------------------^--------------------'

[Buildroot] [PATCH 1/2] package/f2fs-tools: add host package

[Thomas Petazzoni]

Hello,

On Fri, 26 Oct 2018 22:00:15 +0200, Grzegorz Blach wrote:
> This package is useful to create f2fs filesystem during build process.
> 
> Signed-off-by: Grzegorz Blach <grzegorz@blach.pl>

Thanks, I have applied, after adding --without-selinux --without-blkid
to HOST_F2FS_TOOLS_CONF_OPTS. --without-blkid was suggested by Yann.
However, contrary to Yann, I don't think we should unconditionally
enable SELinux support, so I've added a --without-selinux.

Thanks,

Thomas
-- 
Thomas Petazzoni, CTO, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com

[Buildroot] [PATCH 1/2] package/f2fs-tools: add host package

[Thomas Petazzoni]

Hello,

On Wed, 31 Oct 2018 22:21:28 +0100, Yann E. MORIN wrote:

> I don't think that libblkid is needed for the host variant, so we should
> probably explicitly disable it. On the other hand, libblkid is always
> built by host-util-linux.

Agreed, I've added --without-blkid.

> Also, we do have host-libselinux, so wyou may want to also enable that
> unconditionally.

I don't really agree here. We try to build only a minimal set of
dependencies, so we shouldn't build against host-libselinux by default.
Yes, solving that properly requires introducing Config.in options for
host packages :-)

Thomas
-- 
Thomas Petazzoni, CTO, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com

[Buildroot] [PATCH 2/2] fs/f2fs: add support for creating a f2fs image

[Thomas Petazzoni]

Hello,

On Fri, 26 Oct 2018 22:00:16 +0200, Grzegorz Blach wrote:
> This patch makes possible to create rootfs image using f2fs filesystem.
> 
> Signed-off-by: Grzegorz Blach <grzegorz@blach.pl>

I have applied, after doing a number of changes, mainly splitting into
separate patches, as suggested by Yann E. Morin.

However, now that you have added F2FS support, it would be good if you
could add a test in our test suite for this filesystem. Look at
support/testing/tests/fs/ for the other filesystem tests that we have.
Could you add something like this ?

> +config BR2_TARGET_ROOTFS_F2FS_COLD_FILES
> +	string "extension list for cold files"

Any reason for having added this option for cold files, but not the
symmetric option for hot files ?

> +	help
> +	  Specify a file extension list in order f2fs to treat them
> +	  as cold files. The default list includes most of multimedia
> +	  file extensions such as jpg, gif, mpeg, mkv, and so on.

I've seen this after committing, but the help text of mkfs.f2fs seems
to imply that the list of extensions should be comma separated. If
that's the case, it should be mentioned in the help text, because most
Buildroot options use space-separated lists, not comma-separated ones.

> +config BR2_TARGET_ROOTFS_F2FS_OVERPROVISION
> +	int "size for overprovision area (0 for auto calculation)"

Actually 0 is not auto-calculation. 0 will not pass any -O option, and
therefore mkfs.f2fs will use its default of 5%.

Also, this option doesn't give the size, but the ratio.

I've fixed both aspects when committing.

> +	dd if=/dev/zero of=$@ bs=1 count=0 seek=$(F2FS_SIZE)

I've replaced by a truncate, as suggested by Yann.

Thanks!

Thomas
-- 
Thomas Petazzoni, CTO, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com

[Buildroot] [PATCH 2/2] fs/f2fs: add support for creating a f2fs image

[Grzegorz Blach]

On 11/3/18 3:48 PM, Thomas Petazzoni wrote:
> Hello,
> 
> On Fri, 26 Oct 2018 22:00:16 +0200, Grzegorz Blach wrote:
>> This patch makes possible to create rootfs image using f2fs filesystem.
>>
>> Signed-off-by: Grzegorz Blach <grzegorz@blach.pl>
> 
> I have applied, after doing a number of changes, mainly splitting into
> separate patches, as suggested by Yann E. Morin.
> 
> However, now that you have added F2FS support, it would be good if you
> could add a test in our test suite for this filesystem. Look at
> support/testing/tests/fs/ for the other filesystem tests that we have.
> Could you add something like this ?
> 

Ok, I'll write this tests tomorrow.


>> +config BR2_TARGET_ROOTFS_F2FS_COLD_FILES
>> +	string "extension list for cold files"
> 
> Any reason for having added this option for cold files, but not the
> symmetric option for hot files ?
> 

I've missed hot files because manual page don't says anything about 
them.  I'll add a patch for hot files too.


>> +	help
>> +	  Specify a file extension list in order f2fs to treat them
>> +	  as cold files. The default list includes most of multimedia
>> +	  file extensions such as jpg, gif, mpeg, mkv, and so on.
> 
> I've seen this after committing, but the help text of mkfs.f2fs seems
> to imply that the list of extensions should be comma separated. If
> that's the case, it should be mentioned in the help text, because most
> Buildroot options use space-separated lists, not comma-separated ones.
> 
>> +config BR2_TARGET_ROOTFS_F2FS_OVERPROVISION
>> +	int "size for overprovision area (0 for auto calculation)"
> 
> Actually 0 is not auto-calculation. 0 will not pass any -O option, and
> therefore mkfs.f2fs will use its default of 5%.
> 

mkfs.f2fs says that default overprovision ratio is 5%, but in manual 
page you can read `If not specified, the best number will be assigned 
automatically accoring to the partition size`. This is a bit confusing.
After reading source code I'm sure if -o option is omitted or set to 0,
overprovision ratio is auto calculated.


> Also, this option doesn't give the size, but the ratio.
> 
> I've fixed both aspects when committing.
> 
>> +	dd if=/dev/zero of=$@ bs=1 count=0 seek=$(F2FS_SIZE)
> 
> I've replaced by a truncate, as suggested by Yann.
> 
> Thanks!
> 
> Thomas
>