Provided by: freebsd-manpages_12.2-1_all 
NAME
sbuf, sbuf_new, sbuf_new_auto, sbuf_new_for_sysctl, sbuf_clear, sbuf_get_flags, sbuf_set_flags,
sbuf_clear_flags, sbuf_setpos, sbuf_bcat, sbuf_bcopyin, sbuf_bcpy, sbuf_cat, sbuf_copyin, sbuf_cpy,
sbuf_printf, sbuf_vprintf, sbuf_putc, sbuf_set_drain, sbuf_trim, sbuf_error, sbuf_finish, sbuf_data,
sbuf_len, sbuf_done, sbuf_delete, sbuf_start_section, sbuf_end_section, sbuf_hexdump, sbuf_putbuf — safe
string composition
SYNOPSIS
#include <sys/types.h>
#include <sys/sbuf.h>
typedef int (sbuf_drain_func) (void *arg, const char *data, int len);
struct sbuf *
sbuf_new(struct sbuf *s, char *buf, int length, int flags);
struct sbuf *
sbuf_new_auto(void);
void
sbuf_clear(struct sbuf *s);
int
sbuf_get_flags(struct sbuf *s);
void
sbuf_set_flags(struct sbuf *s, int flags);
void
sbuf_clear_flags(struct sbuf *s, int flags);
int
sbuf_setpos(struct sbuf *s, int pos);
int
sbuf_bcat(struct sbuf *s, const void *buf, size_t len);
int
sbuf_bcpy(struct sbuf *s, const void *buf, size_t len);
int
sbuf_cat(struct sbuf *s, const char *str);
int
sbuf_cpy(struct sbuf *s, const char *str);
int
sbuf_printf(struct sbuf *s, const char *fmt, ...);
int
sbuf_vprintf(struct sbuf *s, const char *fmt, va_list ap);
int
sbuf_putc(struct sbuf *s, int c);
void
sbuf_set_drain(struct sbuf *s, sbuf_drain_func *func, void *arg);
int
sbuf_trim(struct sbuf *s);
int
sbuf_error(struct sbuf *s);
int
sbuf_finish(struct sbuf *s);
char *
sbuf_data(struct sbuf *s);
ssize_t
sbuf_len(struct sbuf *s);
int
sbuf_done(struct sbuf *s);
void
sbuf_delete(struct sbuf *s);
void
sbuf_start_section(struct sbuf *s, ssize_t *old_lenp);
ssize_t
sbuf_end_section(struct sbuf *s, ssize_t old_len, size_t pad, int c);
void
sbuf_hexdump(struct sbuf *sb, void *ptr, int length, const char *hdr, int flags);
void
sbuf_putbuf(struct sbuf *s);
#ifdef _KERNEL
#include <sys/types.h>
#include <sys/sbuf.h>
int
sbuf_bcopyin(struct sbuf *s, const void *uaddr, size_t len);
int
sbuf_copyin(struct sbuf *s, const void *uaddr, size_t len);
#include <sys/sysctl.h>
struct sbuf *
sbuf_new_for_sysctl(struct sbuf *s, char *buf, int length, struct sysctl_req *req);
#endif /* _KERNEL */
DESCRIPTION
The sbuf family of functions allows one to safely allocate, compose and release strings in kernel or user
space.
Instead of arrays of characters, these functions operate on structures called sbufs, defined in
<sys/sbuf.h>.
Any errors encountered during the allocation or composition of the string will be latched in the data
structure, making a single error test at the end of the composition sufficient to determine success or
failure of the entire process.
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:
SBUF_FIXEDLEN The storage buffer is fixed at its initial size. Attempting to extend the sbuf beyond
this size results in an overflow condition.
SBUF_AUTOEXTEND This indicates that the storage buffer may be extended as necessary, so long as
resources allow, to hold additional data.
SBUF_INCLUDENUL This causes the final nulterm byte to be counted in the length of the data.
SBUF_DRAINTOEOR Treat top-level sections started with sbuf_start_section() as a record boundary marker
that will be used during drain operations to avoid records being split. If a record
grows sufficiently large such that it fills the sbuf and therefore cannot be drained
without being split, an error of EDEADLK is set.
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_new_auto() function is a shortcut for creating a completely dynamic sbuf. It is the equivalent
of calling sbuf_new() with values NULL, NULL, 0, and SBUF_AUTOEXTEND.
The sbuf_new_for_sysctl() function will set up an sbuf with a drain function to use SYSCTL_OUT() when the
internal buffer fills. Note that if the various functions which append to an sbuf are used while a non-
sleepable lock is held, the user buffer should be wired using sysctl_wire_old_buffer().
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_get_flags() function returns the current user flags. The sbuf_set_flags() and sbuf_get_flags()
functions set or clear one or more user flags, respectively. The user flags are described under the
sbuf_new() function.
The sbuf_setpos() function sets the sbuf's end position to pos, which is a value between zero and the
current position in the buffer. It can only truncate the sbuf to 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_set_drain() function sets a drain function func for the sbuf, and records a pointer arg to be
passed to the drain on callback. The drain function cannot be changed while sbuf_len is non-zero.
The registered drain function sbuf_drain_func will be called with the argument arg provided to
sbuf_set_drain(), a pointer data to a byte string that is the contents of the sbuf, and the length len of
the data. If the drain function exists, it will be called when the sbuf internal buffer is full, or on
behalf of sbuf_finish(). The drain function may drain some or all of the data, but must drain at least 1
byte. The return value from the drain function, if positive, indicates how many bytes were drained. If
negative, the return value indicates the negative error code which will be returned from this or a later
call to sbuf_finish(). The returned drained length cannot be zero. To do unbuffered draining,
initialize the sbuf with a two-byte buffer. The drain will be called for every byte added to the sbuf.
The sbuf_bcopyin(), sbuf_copyin(), sbuf_trim(), and sbuf_data() functions cannot be used on an sbuf with
a drain.
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_error() function returns any error value that the sbuf may have accumulated, either from the
drain function, or ENOMEM if the sbuf overflowed. This function is generally not needed and instead the
error code from sbuf_finish() is the preferred way to discover whether an sbuf had an error.
The sbuf_finish() function will call the attached drain function if one exists until all the data in the
sbuf is flushed. If there is no attached drain, sbuf_finish() NUL-terminates the sbuf. In either case
it marks the sbuf as finished, which means that it may no longer be modified using sbuf_setpos(),
sbuf_cat(), sbuf_cpy(), sbuf_printf() or sbuf_putc(), until sbuf_clear() is used to reset the sbuf.
The sbuf_data() function returns the actual string; sbuf_data() only works on a finished sbuf. The
sbuf_len() function returns the length of the string. For an sbuf with an attached drain, sbuf_len()
returns the length of the un-drained data. sbuf_done() returns non-zero if the sbuf is finished.
The sbuf_start_section() and sbuf_end_section() functions may be used for automatic section alignment.
The arguments pad and c specify the padding size and a character used for padding. The arguments
old_lenp and old_len are to save and restore the current section length when nested sections are used.
For the top level section NULL and -1 can be specified for old_lenp and old_len respectively.
The sbuf_hexdump() function prints an array of bytes to the supplied sbuf, along with an ASCII
representation of the bytes if possible. See the hexdump(3) man page for more details on the interface.
The sbuf_putbuf() function printfs the sbuf to stdout if in userland, and to the console and log if in
the kernel. It does not drain the buffer or update any pointers.
NOTES
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().
Drains in user-space will not always function as indicated. While the drain function will be called
immediately on overflow from the sbuf_putc, sbuf_bcat, sbuf_cat functions, sbuf_printf and sbuf_vprintf
currently have no way to determine whether there will be an overflow until after it occurs, and cannot do
a partial expansion of the format string. Thus when using libsbuf the buffer may be extended to allow
completion of a single printf call, even though a drain is attached.
RETURN VALUES
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_bcat(), sbuf_cat(), sbuf_cpy(), sbuf_printf(), sbuf_putc(), and sbuf_trim() functions all return
-1 if the buffer overflowed, and zero otherwise.
The sbuf_error() function returns a non-zero value if the buffer has an overflow or drain error, and zero
otherwise.
The sbuf_len() function returns -1 if the buffer overflowed.
The sbuf_copyin() function returns -1 if copying string from userland failed, and number of bytes copied
otherwise.
The sbuf_end_section() function returns the section length or -1 if the buffer has an error.
The sbuf_finish(9) function (the kernel version) returns ENOMEM if the sbuf overflowed before being
finished, or returns the error code from the drain if one is attached.
The sbuf_finish(3) function (the userland version) will return zero for success and -1 and set errno on
error.
EXAMPLES
#include <sys/types.h>
#include <sys/sbuf.h>
struct sbuf *sb;
sb = sbuf_new_auto();
sbuf_cat(sb, "Customers found:\n");
TAILQ_FOREACH(foo, &foolist, list) {
sbuf_printf(sb, " %4d %s\n", foo->index, foo->name);
sbuf_printf(sb, " Address: %s\n", foo->address);
sbuf_printf(sb, " Zip: %s\n", foo->zipcode);
}
if (sbuf_finish(sb) != 0) /* Check for any and all errors */
err(1, "Could not generate message");
transmit_msg(sbuf_data(sb), sbuf_len(sb));
sbuf_delete(sb);
SEE ALSO
hexdump(3), printf(3), strcat(3), strcpy(3), copyin(9), copyinstr(9), printf(9)
HISTORY
The sbuf family of functions first appeared in FreeBSD 4.4.
AUTHORS
The sbuf family of functions was designed by Poul-Henning Kamp <phk@FreeBSD.org> and implemented by
Dag-Erling Smørgrav <des@FreeBSD.org>. Additional improvements were suggested by Justin T. Gibbs
<gibbs@FreeBSD.org>. Auto-extend support added by Kelly Yancey <kbyanc@FreeBSD.org>. Drain
functionality added by Matthew Fleming <mdf@FreeBSD.org>.
This manual page was written by Dag-Erling Smørgrav <des@FreeBSD.org>.
Debian August 26, 2020 SBUF(9)