Definition of `struct sbuf` in `/sys/sys/sbuf.h`:

struct sbuf {
	char		*s_buf;		/* storage buffer */
	sbuf_drain_func	*s_drain_func;	/* drain function */
	void		*s_drain_arg;	/* user-supplied drain argument */
	int		 s_error;	/* current error code */
	ssize_t		 s_size;	/* size of storage buffer */
	ssize_t		 s_len;		/* current length of string */
#define	SBUF_FIXEDLEN	0x00000000	/* fixed length buffer (default) */
#define	SBUF_AUTOEXTEND	0x00000001	/* automatically extend buffer */
#define	SBUF_INCLUDENUL	0x00000002	/* nulterm byte is counted in len */
#define	SBUF_USRFLAGMSK	0x0000ffff	/* mask of flags the user may specify */
#define	SBUF_DYNAMIC	0x00010000	/* s_buf must be freed */
#define	SBUF_FINISHED	0x00020000	/* set by sbuf_finish() */
#define	SBUF_DYNSTRUCT	0x00080000	/* sbuf must be freed */
#define	SBUF_INSECTION	0x00100000	/* set by sbuf_start_section() */
	int		 s_flags;	/* flags */
	ssize_t		 s_sect_len;	/* current length of section */
};

All sizes and lengths, such as `s_size`, are of type `ssize_t`.

However some functions in `sys/kern/subr_sbuf.c` incorrectly treat these sizes as `int` which could lead to unexpected truncation on platforms where `sizeof(int)` !== `sizeof(ssize_t)`:

struct sbuf *
sbuf_new(struct sbuf *s, char *buf, int length, int flags)
{
    ...
    sbuf_newbuf(s, buf, length, flags);
    ...
}

static struct sbuf *
sbuf_newbuf(struct sbuf *s, char *buf, int length, int flags)
{
    ...
    s->s_size = length;
    ...
}