Re: [PATCH v3 2/6] selftests/liveupdate: add helper functions for memfd tests

[Zhu Yanjun <yanjun.zhu@linux.dev>]

在 2026/4/5 0:34, Pratyush Yadav 写道:
> On Sat, Apr 04 2026, Zhu Yanjun wrote:
>
>> 在 2026/4/4 3:24, Pratyush Yadav 写道:
>>> From: "Pratyush Yadav (Google)" <pratyush@kernel.org>
>>> Add some helper functions that will be used by memfd tests. This moves
>>> some of the complexity out of the test itself, which results in better
>>> test readability and less code duplication.
>>> Reviewed-by: Mike Rapoport (Microsoft) <rppt@kernel.org>
>>> Signed-off-by: Pratyush Yadav <ptyadav@amazon.de>
>>> Signed-off-by: Pratyush Yadav (Google) <pratyush@kernel.org>
>>> ---
>>>    .../selftests/liveupdate/luo_test_utils.c     | 191 +++++++++++++++++-
>>>    .../selftests/liveupdate/luo_test_utils.h     |  10 +
>>>    2 files changed, 200 insertions(+), 1 deletion(-)
>>> diff --git a/tools/testing/selftests/liveupdate/luo_test_utils.c
>>> b/tools/testing/selftests/liveupdate/luo_test_utils.c
>>> index 3c8721c505df..ceb918ef9813 100644
>>> --- a/tools/testing/selftests/liveupdate/luo_test_utils.c
>>> +++ b/tools/testing/selftests/liveupdate/luo_test_utils.c
>>> @@ -1,8 +1,12 @@
>>>    // SPDX-License-Identifier: GPL-2.0-only
>>>      /*
>>> - * Copyright (c) 2025, Google LLC.
>>> + * Copyright (c) 2025-2026, Google LLC.
>>>     * Pasha Tatashin <pasha.tatashin@soleen.com>
>>> + * Pratyush Yadav (Google) <pratyush@kernel.org>
>>> + *
>>> + * Copyright (C) 2025 Amazon.com Inc. or its affiliates.
>>> + * Pratyush Yadav <ptyadav@amazon.de>
>>>     */
>>>      #define _GNU_SOURCE
>>> @@ -20,9 +24,194 @@
>>>    #include <sys/stat.h>
>>>    #include <errno.h>
>>>    #include <stdarg.h>
>>> +#include <sys/vfs.h>
>>> +#include <linux/magic.h>
>>>      #include "luo_test_utils.h"
>>>    +int cwd_is_tmpfs(void)
>>> +{
>>> +	struct statfs buf;
>>> +
>>> +	if (statfs(".", &buf) < 0)
>>> +		return -errno;
>>> +
>>> +	return buf.f_type == TMPFS_MAGIC;
>>> +}
>>> +
>>> +/* Read exactly specified size from fd. Any less results in error. */
>>> +int read_size(int fd, char *buffer, size_t size)
>>> +{
>>> +	size_t remain = size;
>>> +	ssize_t bytes_read;
>>> +
>>> +	while (remain) {
>> while (remain > 0) ?
> I don't think it is needed. bytes_read will always be smaller than or
> equal to remain, so remain will never go below 0 anyway. And while
> (remain) is nicer to read.

If a wrong number is transferred, this makes remain less than 0. Then 
this loop will run again and again.

This while (remain > 0) will avoid this kind of scenario.

ZhuYanjun

>
>>> +		bytes_read = read(fd, buffer, remain);
>>> +		if (bytes_read == 0)
>>> +			return -ENODATA;
>>> +		if (bytes_read < 0) {
>>> +			if (errno == EINTR)
>>> +				continue;
>>> +			else
>>> +				return -errno;
>>> +		}
>>> +
>>> +		remain -= bytes_read;
>>> +		buffer += bytes_read;
>>> +	}
>>> +
>>> +	return 0;
>>> +}
>>> +
> [...]
>
-- 
Best Regards,
Yanjun.Zhu