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Re: [RFC PATCH v2 1/2] util: Add thread-safe qemu_strerror() function
From: |
Alex Bennée |
Subject: |
Re: [RFC PATCH v2 1/2] util: Add thread-safe qemu_strerror() function |
Date: |
Thu, 30 Mar 2023 15:04:49 +0100 |
User-agent: |
mu4e 1.10.0; emacs 29.0.60 |
Yohei Kojima <y-koj@outlook.jp> writes:
> Add qemu_strerror() which follows the POSIX specification for
> strerror(). While strerror() is not guaranteed to be thread-safe, this
> function is thread-safe.
>
> This function is added to solve the following issue:
> https://gitlab.com/qemu-project/qemu/-/issues/416
If you tag this as:
Fixes: https://gitlab.com/qemu-project/qemu/-/issues/416
then it will auto clear when merged.
>
> Signed-off-by: Yohei Kojima <y-koj@outlook.jp>
> ---
> include/qemu/cutils.h | 20 +++++++++++++++++++
> util/cutils.c | 45 +++++++++++++++++++++++++++++++++++++++++++
> 2 files changed, 65 insertions(+)
>
> diff --git a/include/qemu/cutils.h b/include/qemu/cutils.h
> index 92c436d8c7..0bcae0049a 100644
> --- a/include/qemu/cutils.h
> +++ b/include/qemu/cutils.h
> @@ -117,6 +117,26 @@ int stristart(const char *str, const char *val, const
> char **ptr);
> * Returns: length of @s in bytes, or @max_len, whichever is smaller.
> */
> int qemu_strnlen(const char *s, int max_len);
> +/**
> + * qemu_strerror:
> + * @errnum: error number
> + *
> + * Return the pointer to a string that describes errnum, like
> + * strerror(). This function is thread-safe because the buffer for
> + * returned string is allocated per thread.
> + *
> + * This function is thread-safe, but not reentrant. In other words,
> + * if a thread is interrupted by a signal in this function, and the
> + * thread calls this function again in the signal handling, then
> + * the result might be corrupted.
> + *
> + * This function has the same behaviour as the POSIX strerror()
> + * function.
> + *
> + * Returns: the pointer to an error description, or an
> + * "Unknown error nnn" message if errnum is invalid.
> + */
> +char *qemu_strerror(int errnum);
> /**
> * qemu_strsep:
> * @input: pointer to string to parse
> diff --git a/util/cutils.c b/util/cutils.c
> index 5887e74414..3d14f50c75 100644
> --- a/util/cutils.c
> +++ b/util/cutils.c
> @@ -131,6 +131,51 @@ int qemu_strnlen(const char *s, int max_len)
> return i;
> }
>
> +/**
> + * It assumes the length of error descriptions are at most 1024.
> + * The concern of write buffer overflow is cared by strerror_r().
> + */
> +static __thread char qemu_strerror_buf[1024];
> +
> +#if (_POSIX_C_SOURCE >= 200112L) && ! _GNU_SOURCE
> +/**
> + * In POSIX.1-2001 and after, the return type of strerror_r is int, but
> + * glibc overrides the definition of strerror_r to the old strerror_r
> + * if _GNU_SOURCE is defined. This condition handles it.
> + */
> +
> +char *qemu_strerror(int errnum)
> +{
> + int is_error = strerror_r(errnum, qemu_strerror_buf, 1024);
> +
> + if (is_error == 0) return qemu_strerror_buf;
> +
> + /**
> + * handle the error occured in strerror_r
> + *
> + * If is_error is greater than 0, errno might not be updated by
> + * strerror_r. Otherwise, errno is updated.
> + */
> + if (is_error > 0) errno = is_error;
> +
> + strncpy(qemu_strerror_buf, "Error %d occured\n", errno);
> + return qemu_strerror_buf;
> +}
> +#else
> +/**
> + * In glibc, the return type of strerror_r is char* if _GNU_SOURCE
> + * is defined. In this case, strerror_r returns qemu_strerror_buf iff
> + * some error occured in strerror_r, and otherwise it returns a pointer
> + * to the pre-defined description for errnum.
> + *
> + * This is the same behaviour until POSIX.1-2001.
> + */
> +char *qemu_strerror(int errnum)
> +{
> + return strerror_r(errnum, qemu_strerror_buf, 1024);
> +}
> +#endif
> +
> char *qemu_strsep(char **input, const char *delim)
> {
> char *result = *input;
--
Alex Bennée
Virtualisation Tech Lead @ Linaro