From a2f2f3f5ee1bb9c953f098f019c3ad09657cba38 Mon Sep 17 00:00:00 2001 From: Douglas Anderson Date: Fri, 29 Jan 2021 16:35:24 -0800 Subject: linux_mtd: Disable buffering on the mtd device We open the device node for the MTD device with this: dev_fp = fopen(dev_path, "r+") In C fopen() is allowed to provide _buffered_ access to the file. That means that the standard library is allowed to read ahead and/or return cached data. That's really not what we want for something like this. Let's turn it off. This fixes a problem where flashrom would sometimes fail to "verify" that it erased the flash. The error message would look something like this: Erasing and writing flash chip... FAILED at 0x0000e220! Expected=0xff, Found=0xe9, failed byte count from 0x0000e200-0x0000e2ff: 0xdc failed byte count from 0x0000e000-0x0000efff: 0xffffffff ERASE_FAILED FAILED! Uh oh. Erase/write failed. Checking if anything changed. After the failure I could read the flash device with a new invocation of flashrom and I would see that, indeed, the erase had worked. Tracing in the kernel showed that when the failure happened we saw a pattern that looked like this: * Read 0x0b00 bytes starting at 0x0000d000 * Read 0x1000 bytes starting at 0x0000db00 * Erase 0x1000 bytes starting at 0x0000e000 ...and then there was _not_ a read after the erase. It can be assumed that, since userspace had already read 0xdb00 - 0xeaff that it was looking at old buffered data after the erase. Signed-off-by: Douglas Anderson Change-Id: I989afd83a33013b2756a0090d6b08245613215c6 Reviewed-on: https://review.coreboot.org/c/flashrom/+/50155 Reviewed-by: Hung-Te Lin Reviewed-by: Patrick Rudolph Reviewed-by: Angel Pons Tested-by: build bot (Jenkins) --- linux_mtd.c | 4 ++++ 1 file changed, 4 insertions(+) diff --git a/linux_mtd.c b/linux_mtd.c index d2df95ef2..22702e904 100644 --- a/linux_mtd.c +++ b/linux_mtd.c @@ -340,6 +340,10 @@ static int linux_mtd_setup(int dev_num) msg_perr("Cannot open file stream for %s\n", dev_path); goto linux_mtd_setup_exit; } + ret = setvbuf(dev_fp, NULL, _IONBF, 0); + if (ret) + msg_pwarn("Failed to set MTD device to unbuffered: %d\n", ret); + msg_pinfo("Opened %s successfully\n", dev_path); ret = 0; -- cgit v1.2.3