Hi, > -----Original Message----- > From: openwrt-devel [mailto:openwrt-devel-boun...@lists.openwrt.org] > On Behalf Of Thibaut VARÈNE > Sent: Sonntag, 17. Mai 2020 20:29 > To: openwrt-devel@lists.openwrt.org > Cc: Thibaut VARÈNE <ha...@slashdirt.org> > Subject: [OpenWrt-Devel] [PATCH] package/base-files: caldata: work around > dd's limitation > > tl;dr: dd will silently truncate the output if reading from special files > (e.g. sysfs > attributes) with a too large bs parameter. > > This problem was exposed on some RouterBOARD ipq40xx devices which use > a caldata payload which is larger than PAGE_SIZE, contrary to all other > currently supported RouterBOARD devices: the caldata would fail to properly > load with the current scripts. > > Background: dd doesn't seem to correctly handle read() results that return > less than requested data. sysfs attributes have a kernel exchange buffer > which is at most PAGE_SIZE big, so only 1 page can be read() at a time. In > this > case, if bs is larger than PAGE_SIZE, dd will silently truncate blocks to > PAGE_SIZE. With the current scripts using bs=<size> count=1, the data is > truncated to PAGE_SIZE as soon as the requested <size> exceeds this value. > > This commit works around this problem by using `cat` in the caldata routines > that can read from a file (routines that read from mtd devices are > untouched). cat correctly handles partial read requests. The output is then > piped to dd with the same parameters as before, to ensure that the resulting > file remains exactly the same. > > This is a simple workaround, the downside is that it uses a pipe and one more > executable, and therefore has a larger memory footprint and is slower. This > is deemed acceptable considering these routines are only used at boot time. > > Tested-by: Robert Marko <robima...@gmail.com> > Signed-off-by: Thibaut VARÈNE <ha...@slashdirt.org> > --- > package/base-files/Makefile | 2 +- > package/base-files/files/lib/functions/caldata.sh | 6 +++--- > 2 files changed, 4 insertions(+), 4 deletions(-) > > diff --git a/package/base-files/Makefile b/package/base-files/Makefile index > d8e7c31878..5fb275533d 100644 > --- a/package/base-files/Makefile > +++ b/package/base-files/Makefile > @@ -12,7 +12,7 @@ include $(INCLUDE_DIR)/version.mk include > $(INCLUDE_DIR)/feeds.mk > > PKG_NAME:=base-files > -PKG_RELEASE:=220 > +PKG_RELEASE:=221 > PKG_FLAGS:=nonshared > > PKG_FILE_DEPENDS:=$(PLATFORM_DIR)/ > $(GENERIC_PLATFORM_DIR)/base-files/ > diff --git a/package/base-files/files/lib/functions/caldata.sh b/package/base- > files/files/lib/functions/caldata.sh > index 6862da7164..8b031e29cd 100644 > --- a/package/base-files/files/lib/functions/caldata.sh > +++ b/package/base-files/files/lib/functions/caldata.sh > @@ -64,7 +64,7 @@ caldata_from_file() { > > [ -n "$target" ] || target=/lib/firmware/$FIRMWARE > > - dd if=$source of=$target iflag=skip_bytes bs=$count skip=$offset > count=1 2>/dev/null || \ > + cat $source | dd of=$target iflag=skip_bytes bs=$count skip=$offset
These lines should receive a short comment directly next to the code, as
otherwise somebody will "improve" this by removing the cat again when nobody
remembers your patch anymore. I already see a "remove useless cat" commit title
in front of my eye :-)
Best
Adrian
> +count=1 2>/dev/null || \
> caldata_die "failed to extract calibration data from $source"
> }
>
> @@ -74,12 +74,12 @@ caldata_sysfsload_from_file() {
> local count=$(($3))
>
> # test extract to /dev/null first
> - dd if=$source of=/dev/null iflag=skip_bytes bs=$count skip=$offset
> count=1 2>/dev/null || \
> + cat $source | dd of=/dev/null iflag=skip_bytes bs=$count
> skip=$offset
> +count=1 2>/dev/null || \
> caldata_die "failed to extract calibration data from $source"
>
> # can't fail now
> echo 1 > /sys/$DEVPATH/loading
> - dd if=$source of=/sys/$DEVPATH/data iflag=skip_bytes bs=$count
> skip=$offset count=1 2>/dev/null
> + cat $source | dd of=/sys/$DEVPATH/data iflag=skip_bytes bs=$count
> +skip=$offset count=1 2>/dev/null
> echo 0 > /sys/$DEVPATH/loading
> }
>
> --
> 2.11.0
>
>
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