On 10/26/2012 03:51 PM, Matt Fleming wrote:
From: Jeremy Kerr<[email protected]>
A write to an efivarfs file will not always result in a variable of
'count' size after the EFI SetVariable() call. We may have appended to
the existing data (ie, with the EFI_VARIABLE_APPEND_WRITE attribute), or
even have deleted the variable (with an authenticated variable update,
with a zero datasize).
This change re-reads the updated variable from firmware, to check for
size changes and deletions. In the latter case, we need to drop the
dentry.
File lingers after deletion with efivarfs_write_file.
Reproduced on QEMU/OVMF, 3.8-rc vanilla kernel.
Choosing the variable RTC because it's been generated by OVMF when
mounting.
Steps to reproduce (bash commandline):
# P=/sys/firmware/efi/efivars
# VAR=$P/RTC-378d7b65-8da9-4773-b6e4-a47826a833e1
# mount -t efivarfs - $P
# stat -c'%s %h' $VAR
8 1
# dd if=/dev/zero of=$VAR bs=4 count=1 conv=notrunc 2>&-
# stat -c'%s %h' $VAR
8 0
Writing four null bytes to $VAR should delete it.
--
Lingzhu Xiang
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