Re: [PATCH v6 2/4] util: Introduce read_file() and read_file_integer() function

[Stefano Brivio <sbrivio@redhat.com>]

On Fri, 17 Oct 2025 14:28:36 +0800
Yumei Huang <yuhuang@redhat.com> wrote:

> Signed-off-by: Yumei Huang <yuhuang@redhat.com>
> ---
>  util.c | 84 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
>  util.h |  8 ++++++
>  2 files changed, 92 insertions(+)
> 
> diff --git a/util.c b/util.c
> index c492f90..5c8c4bc 100644
> --- a/util.c
> +++ b/util.c
> @@ -579,6 +579,90 @@ int write_file(const char *path, const char *buf)
>  	return len == 0 ? 0 : -1;
>  }
>  
> +/**
> + * read_file() - Read contents of file into a buffer
> + * @path:	File to read
> + * @buf:	Buffer to store file contents
> + * @buf_size:	Size of buffer
> + *
> + * Return: number of bytes read on success, -1 on any error, -2 on truncation
> +*/
> +ssize_t read_file(const char *path, char *buf, size_t buf_size)
> +{
> +	int fd = open(path, O_RDONLY | O_CLOEXEC);
> +	size_t total_read = 0;
> +	ssize_t rc;
> +
> +	if (fd < 0) {
> +		warn_perror("Could not open %s", path);
> +		return -1;
> +	}
> +
> +	while (total_read < buf_size) {
> +		rc = read(fd, buf + total_read, buf_size - total_read);
> +
> +		if (rc < 0) {
> +			warn_perror("Couldn't read from %s", path);
> +			close(fd);
> +			return -1;
> +		}
> +
> +		if (rc == 0)
> +			break;
> +
> +		total_read += rc;
> +	}
> +
> +	close(fd);
> +
> +	if (total_read == buf_size) {
> +		warn("File %s truncated, buffer too small", path);
> +		return -2;
> +	}
> +
> +	buf[total_read] = '\0';
> +
> +	return total_read;
> +}
> +
> +/**
> + * read_file_integer() - Read an integer value from a file
> + * @path: File to read
> + * @fallback: Default value if file can't be read
> + *
> + * Return: Integer value, fallback on failure
> +*/
> +intmax_t read_file_integer(const char *path, intmax_t fallback)
> +{
> +	char buf[INTMAX_STRLEN];
> +	ssize_t bytes_read;
> +	intmax_t value;
> +	char *end;
> +
> +	bytes_read = read_file(path, buf, sizeof(buf));
> +
> +	if (bytes_read < 0)
> +		return fallback;
> +
> +	if (bytes_read == 0) {
> +		debug("Empty file %s", path);
> +		return fallback;
> +	}
> +
> +	errno = 0;
> +	value = strtoimax(buf, &end, 10);
> +	if (*end && *end != '\n') {
> +		debug("Invalid format in %s", path);
> +		return fallback;
> +	}
> +	if (errno) {
> +		debug("Invalid value in %s: %s", path, buf);
> +		return fallback;
> +	}
> +
> +	return value;
> +}
> +
>  #ifdef __ia64__
>  /* Needed by do_clone() below: glibc doesn't export the prototype of __clone2(),
>   * use the description from clone(2).
> diff --git a/util.h b/util.h
> index 22eaac5..3f9f296 100644
> --- a/util.h
> +++ b/util.h
> @@ -222,6 +222,8 @@ void pidfile_write(int fd, pid_t pid);
>  int __daemon(int pidfile_fd, int devnull_fd);
>  int fls(unsigned long x);
>  int write_file(const char *path, const char *buf);
> +ssize_t read_file(const char *path, char *buf, size_t buf_size);
> +intmax_t read_file_integer(const char *path, intmax_t fallback);
>  int write_all_buf(int fd, const void *buf, size_t len);
>  int write_remainder(int fd, const struct iovec *iov, size_t iovcnt, size_t skip);
>  int read_all_buf(int fd, void *buf, size_t len);
> @@ -250,6 +252,12 @@ static inline const char *af_name(sa_family_t af)
>  
>  #define UINT16_STRLEN		(sizeof("65535"))
>  
> +/* Each byte expands to at most 3 decimal digits since 0xff == 255.
> + * Plus 2 extra bytes for the sign and null terminator.
> + * See https://stackoverflow.com/a/10536254.

This is not an acceptable form of attribution according to the
CC BY-SA 3.0 terms. See:

  https://stackoverflow.com/help/licensing
  https://creativecommons.org/licenses/by-sa/3.0/

and checksum.h in this tree for some examples of how to combine
different licensing terms in a single file, in a way that's
human-readable but still machine-friendly (for license / compliance
scanners such as REUSE).

As I commented on a previous version, anyway, I don't think we need
this at all. I guess my comment was ignored though.

Note that I didn't review this patch or the rest of this series, yet.

-- 
Stefano