SBUF(9) MidnightBSD Kernel Developer’s Manual SBUF(9)


sbuf, sbuf_new, sbuf_clear, sbuf_setpos, sbuf_bcat, sbuf_bcopyin, sbuf_bcpy, sbuf_cat, sbuf_copyin, sbuf_cpy, sbuf_printf, sbuf_vprintf, sbuf_putc, sbuf_trim, sbuf_overflowed, sbuf_finish, sbuf_data, sbuf_len, sbuf_done, sbuf_delete — safe string formatting


#include <sys/types.h>
#include <sys/sbuf.h>

struct sbuf *

sbuf_new(struct sbuf *s, char *buf, int length, int flags);


sbuf_clear(struct sbuf *s);


sbuf_setpos(struct sbuf *s, int pos);


sbuf_bcat(struct sbuf *s, const void *buf, size_t len);


sbuf_bcopyin(struct sbuf *s, const void *uaddr, size_t len);


sbuf_bcpy(struct sbuf *s, const void *buf, size_t len);


sbuf_cat(struct sbuf *s, const char *str);


sbuf_copyin(struct sbuf *s, const void *uaddr, size_t len);


sbuf_cpy(struct sbuf *s, const char *str);


sbuf_printf(struct sbuf *s, const char *fmt, ...);


sbuf_vprintf(struct sbuf *s, const char *fmt, va_list ap);


sbuf_putc(struct sbuf *s, int c);


sbuf_trim(struct sbuf *s);


sbuf_overflowed(struct sbuf *s);


sbuf_finish(struct sbuf *s);

char *

sbuf_data(struct sbuf *s);


sbuf_len(struct sbuf *s);


sbuf_done(struct sbuf *s);


sbuf_delete(struct sbuf *s);


The sbuf family of functions allows one to safely allocate, construct and release bounded null-terminated strings in kernel space. Instead of arrays of characters, these functions operate on structures called sbufs, defined in <sys/sbuf.h>.

The sbuf_new() function initializes the sbuf pointed to by its first argument. If that pointer is NULL, sbuf_new() allocates a struct sbuf using malloc(9). The buf argument is a pointer to a buffer in which to store the actual string; if it is NULL, sbuf_new() will allocate one using malloc(9). The length is the initial size of the storage buffer. The fourth argument, flags, may be comprised of the following flags:


The storage buffer is fixed at its initial size. Attempting to extend the sbuf beyond this size results in an overflow condition.


This indicates that the storage buffer may be extended as necessary, so long as resources allow, to hold additional data.

Note that if buf is not NULL, it must point to an array of at least length characters. The result of accessing that array directly while it is in use by the sbuf is undefined.

The sbuf_delete() function clears the sbuf and frees any memory allocated for it. There must be a call to sbuf_delete() for every call to sbuf_new(). Any attempt to access the sbuf after it has been deleted will fail.

The sbuf_clear() function invalidates the contents of the sbuf and resets its position to zero.

The sbuf_setpos() function sets the sbuf’s end position to pos, which is a value between zero and one less than the size of the storage buffer. This effectively truncates the sbuf at the new position.

The sbuf_bcat() function appends the first len bytes from the buffer buf to the sbuf.

The sbuf_bcopyin() function copies len bytes from the specified userland address into the sbuf.

The sbuf_bcpy() function replaces the contents of the sbuf with the first len bytes from the buffer buf.

The sbuf_cat() function appends the NUL-terminated string str to the sbuf at the current position.

The sbuf_copyin() function copies a NUL-terminated string from the specified userland address into the sbuf. If the len argument is non-zero, no more than len characters (not counting the terminating NUL) are copied; otherwise the entire string, or as much of it as can fit in the sbuf, is copied.

The sbuf_cpy() function replaces the contents of the sbuf with those of the NUL-terminated string str. This is equivalent to calling sbuf_cat() with a fresh sbuf or one which position has been reset to zero with sbuf_clear() or sbuf_setpos().

The sbuf_printf() function formats its arguments according to the format string pointed to by fmt and appends the resulting string to the sbuf at the current position.

The sbuf_vprintf() function behaves the same as sbuf_printf() except that the arguments are obtained from the variable-length argument list ap.

The sbuf_putc() function appends the character c to the sbuf at the current position.

The sbuf_trim() function removes trailing whitespace from the sbuf.

The sbuf_overflowed() function returns a non-zero value if the sbuf overflowed.

The sbuf_finish() function null-terminates the sbuf and marks it as finished, which means that it may no longer be modified using sbuf_setpos(), sbuf_cat(), sbuf_cpy(), sbuf_printf() or sbuf_putc().

The sbuf_data() and sbuf_len() functions return the actual string and its length, respectively; sbuf_data() only works on a finished sbuf. sbuf_done() returns non-zero if the sbuf is finished.


If an operation caused an sbuf to overflow, most subsequent operations on it will fail until the sbuf is finished using sbuf_finish() or reset using sbuf_clear(), or its position is reset to a value between 0 and one less than the size of its storage buffer using sbuf_setpos(), or it is reinitialized to a sufficiently short string using sbuf_cpy().


The sbuf_new() function returns NULL if it failed to allocate a storage buffer, and a pointer to the new sbuf otherwise.

The sbuf_setpos() function returns −1 if pos was invalid, and zero otherwise.

The sbuf_cat(), sbuf_cpy(), sbuf_printf(), sbuf_putc(), and sbuf_trim() functions all return −1 if the buffer overflowed, and zero otherwise.

The sbuf_overflowed() function returns a non-zero value if the buffer overflowed, and zero otherwise.

The sbuf_data() and sbuf_len() functions return NULL and −1, respectively, if the buffer overflowed.

The sbuf_copyin() function returns −1 if copying string from userland failed, and number of bytes copied otherwise.


printf(3), strcat(3), strcpy(3), copyin(9), copyinstr(9), printf(9)


The sbuf family of functions first appeared in FreeBSD 4.4.


The sbuf family of functions was designed by Poul-Henning Kamp 〈〉 and implemented by Dag-Erling Smørgrav 〈〉. Additional improvements were suggested by Justin T. Gibbs 〈〉. Auto-extend support added by Kelly Yancey 〈〉.

This manual page was written by Dag-Erling Smørgrav 〈〉.

MidnightBSD 0.3 July 9, 2004 MidnightBSD 0.3