[PATCH RFC 2/3] libfile: implement read_fd counterpart to read_file

[Yann Sionneau]

Hello Ahmad,

On 11/20/23 09:37, Ahmad Fatoum wrote:
> Files opened with O_TMPFILE have no name, so read_file can't be used
> with them. Therefore add a read_fd function, which slurps all a file's
> contents into a buffer.
>
> Signed-off-by: Ahmad Fatoum <a.fatoum at pengutronix.de>
> ---
>   include/libfile.h |  2 ++
>   lib/libfile.c     | 44 ++++++++++++++++++++++++++++++++++++++++++++
>   2 files changed, 46 insertions(+)
>
> diff --git a/include/libfile.h b/include/libfile.h
> index a353ccfa9ea9..423e7ffec5b7 100644
> --- a/include/libfile.h
> +++ b/include/libfile.h
> @@ -12,6 +12,8 @@ char *read_file_line(const char *fmt, ...);
>   
>   void *read_file(const char *filename, size_t *size);
>   
> +void *read_fd(int fd, size_t *size);
> +
>   int read_file_2(const char *filename, size_t *size, void **outbuf,
>   		loff_t max_size);
>   
> diff --git a/lib/libfile.c b/lib/libfile.c
> index e53ba08415a2..c257baaa2733 100644
> --- a/lib/libfile.c
> +++ b/lib/libfile.c
> @@ -306,6 +306,50 @@ void *read_file(const char *filename, size_t *size)
>   }
>   EXPORT_SYMBOL(read_file);
>   
> +/**
> + * read_fd - read from a file descriptor to an allocated buffer
> + * @filename:  The file descriptor to read
> + * @size:      After successful return contains the size of the file
> + *
> + * This function reads a file descriptor from offset 0 until EOF to an
> + * allocated buffer.
> + *
> + * Return: The buffer containing the file or NULL on failure
> + */
> +void *read_fd(int fd, size_t *out_size)
> +{
> +	off_t off;
> +	ssize_t ret;
> +	size_t size;
> +	void *buf;
> +
> +	off = lseek(fd, SEEK_CUR, 0);
> +	if (off >= 0) {
> +		size = off;
> +		off = lseek(fd, SEEK_SET, 0);
> +	}
> +	if (off < 0) {
> +		ret = off;
> +		goto close_fd;
> +	}
> +
> +	buf = malloc(size + 3);

Maybe check the return value from malloc()?

Also, it's not clear to me why this +3 is needed and the 3 extra \0, 
maybe an in-code comment would help?

> +	ret = read_full(fd, buf, size);
> +	if (ret < 0) {
> +		free(buf);
> +		goto close_fd;
> +	}
> +
> +	memset(&buf[size], '\0', 3);
> +	*out_size = size;
> +
> +close_fd:
> +	close(fd);
> +
> +	return ret < 0 ? NULL : buf;
> +}
> +EXPORT_SYMBOL(read_fd);
> +
>   /**
>    * write_file - write a buffer to a file
>    * @filename:    The filename to write

Regards,

-- 

Yann