Douglas Anderson has uploaded this change for review. ( https://review.coreboot.org/c/flashrom/+/50155 )
Change subject: WIP: linux_mtd: Disable buffering on the mtd device ......................................................................
WIP: 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.
BRANCH=trogdor BUG=b:178822068 TEST=Loop back and forth writing two BIOS files => no errors
Signed-off-by: Douglas Anderson dianders@chromium.org Change-Id: I989afd83a33013b2756a0090d6b08245613215c6 --- M linux_mtd.c 1 file changed, 4 insertions(+), 0 deletions(-)
git pull ssh://review.coreboot.org:29418/flashrom refs/changes/55/50155/1
diff --git a/linux_mtd.c b/linux_mtd.c index d2df95e..22702e9 100644 --- a/linux_mtd.c +++ b/linux_mtd.c @@ -340,6 +340,10 @@ 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;