Re: [PATCH v4 2/4] util: Introduce read_file() and read_file_integer() function

On Thu, Oct 16, 2025 at 10:34:21AM +0800, Yumei Huang wrote:

Signed-off-by: Yumei Huang --- util.c | 84 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ util.h | 3 +++ 2 files changed, 87 insertions(+)

diff --git a/util.c b/util.c index c492f90..197677e 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 +*/ +int 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_perror("File %s truncated, buffer too small", path); + return -2; + } + + buf[total_read] = '\0'; + + return (int)total_read;

Probably makes more sense for total_read and the return type to be ssize_t.

+} + +/** + * 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]; + char *end;

passt coding style is to list (where possible) local variables in reverse order of line length, so this should go after bytes_read.

+ intmax_t value; + int bytes_read; + + 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..887d795 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); +int 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); @@ -249,6 +251,7 @@ static inline const char *af_name(sa_family_t af) }

#define UINT16_STRLEN (sizeof("65535")) +#define INTMAX_STRLEN (sizeof("-9223372036854775808"))

It's correct for now, and probably for any systems we're likely to run on, but I dislike hard-assuming the size of intmax_t here. I feel like there must be a better way to derive the correct string length, but I haven't figured out what it is yet :(.

/* inet address (- '\0') + port (u16) (- '\0') + ':' + '\0' */ #define SOCKADDR_INET_STRLEN \ -- 2.47.0

-- David Gibson (he or they) | I'll have my music baroque, and my code david AT gibson.dropbear.id.au | minimalist, thank you, not the other way | around. http://www.ozlabs.org/~dgibson