From 7557e7f267e845db5a403139c49f2637f9021992 Mon Sep 17 00:00:00 2001 From: =?UTF-8?q?Thibaut=20VAR=C3=88NE?= Date: Sat, 16 May 2020 22:18:15 +0200 Subject: [PATCH] package/base-files: caldata: work around dd's limitation MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit 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= count=1, the data is truncated to PAGE_SIZE as soon as the requested 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 Signed-off-by: Thibaut VARÈNE --- package/base-files/Makefile | 2 +- package/base-files/files/lib/functions/caldata.sh | 8 +++++--- 2 files changed, 6 insertions(+), 4 deletions(-) diff --git a/package/base-files/Makefile b/package/base-files/Makefile index 5fb275533d..5bf783d0e8 100644 --- a/package/base-files/Makefile +++ b/package/base-files/Makefile @@ -12,7 +12,7 @@ include $(INCLUDE_DIR)/version.mk include $(INCLUDE_DIR)/feeds.mk PKG_NAME:=base-files -PKG_RELEASE:=221 +PKG_RELEASE:=222 PKG_FLAGS:=nonshared PKG_FILE_DEPENDS:=$(PLATFORM_DIR)/ $(GENERIC_PLATFORM_DIR)/base-files/ diff --git a/package/base-files/files/lib/functions/caldata.sh b/package/base-files/files/lib/functions/caldata.sh index 6862da7164..e22c7d27e6 100644 --- a/package/base-files/files/lib/functions/caldata.sh +++ b/package/base-files/files/lib/functions/caldata.sh @@ -64,7 +64,8 @@ caldata_from_file() { [ -n "$target" ] || target=/lib/firmware/$FIRMWARE - dd if=$source of=$target iflag=skip_bytes bs=$count skip=$offset count=1 2>/dev/null || \ + # dd doesn't handle partial reads from special files: use cat + cat $source | dd of=$target iflag=skip_bytes bs=$count skip=$offset count=1 2>/dev/null || \ caldata_die "failed to extract calibration data from $source" } @@ -73,13 +74,14 @@ caldata_sysfsload_from_file() { local offset=$(($2)) local count=$(($3)) + # dd doesn't handle partial reads from special files: use cat # test extract to /dev/null first - dd if=$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 }