freebsd/share/man/man9/sbuf.9

.\"-
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.Dd July 9, 2004
.Dt SBUF 9
.Os
.Sh NAME
.Nm sbuf ,
.Nm sbuf_new ,
.Nm sbuf_clear ,
.Nm sbuf_setpos ,
.Nm sbuf_bcat ,
.Nm sbuf_bcopyin ,
.Nm sbuf_bcpy ,
.Nm sbuf_cat ,
.Nm sbuf_copyin ,
.Nm sbuf_cpy ,
.Nm sbuf_printf ,
.Nm sbuf_vprintf ,
.Nm sbuf_putc ,
.Nm sbuf_trim ,
.Nm sbuf_overflowed ,
.Nm sbuf_finish ,
.Nm sbuf_data ,
.Nm sbuf_len ,
.Nm sbuf_done ,
.Nm sbuf_delete
.Nd safe string formatting
.Sh SYNOPSIS
.In sys/types.h
.In sys/sbuf.h
.Ft struct sbuf *
.Fn sbuf_new "struct sbuf *s" "char *buf" "int length" "int flags"
.Ft void
.Fn sbuf_clear "struct sbuf *s"
.Ft int
.Fn sbuf_setpos "struct sbuf *s" "int pos"
.Ft int
.Fn sbuf_bcat "struct sbuf *s" "const void *buf" "size_t len"
.Ft int
.Fn sbuf_bcopyin "struct sbuf *s" "const void *uaddr" "size_t len"
.Ft int
.Fn sbuf_bcpy "struct sbuf *s" "const void *buf" "size_t len"
.Ft int
.Fn sbuf_cat "struct sbuf *s" "const char *str"
.Ft int
.Fn sbuf_copyin "struct sbuf *s" "const void *uaddr" "size_t len"
.Ft int
.Fn sbuf_cpy "struct sbuf *s" "const char *str"
.Ft int
.Fn sbuf_printf "struct sbuf *s" "const char *fmt" "..."
.Ft int
.Fn sbuf_vprintf "struct sbuf *s" "const char *fmt" "va_list ap"
.Ft int
.Fn sbuf_putc "struct sbuf *s" "int c"
.Ft int
.Fn sbuf_trim "struct sbuf *s"
.Ft int
.Fn sbuf_overflowed "struct sbuf *s"
.Ft void
.Fn sbuf_finish "struct sbuf *s"
.Ft char *
.Fn sbuf_data "struct sbuf *s"
.Ft int
.Fn sbuf_len "struct sbuf *s"
.Ft int
.Fn sbuf_done "struct sbuf *s"
.Ft void
.Fn sbuf_delete "struct sbuf *s"
.Sh DESCRIPTION
The
.Nm
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
.Fa sbufs ,
defined in
.In sys/sbuf.h .
.Pp
The
.Fn sbuf_new
function initializes the
.Fa sbuf
pointed to by its first argument.
If that pointer is
.Dv NULL ,
.Fn sbuf_new
allocates a
.Vt struct sbuf
using
.Xr malloc 9 .
The
.Fa buf
argument is a pointer to a buffer in which to store the actual string;
if it is
.Dv NULL ,
.Fn sbuf_new
will allocate one using
.Xr malloc 9 .
The
.Fa length
is the initial size of the storage buffer.
The fourth argument,
.Fa flags ,
may be comprised of the following flags:
.Bl -tag -width ".Dv SBUF_AUTOEXTEND"
.It Dv SBUF_FIXEDLEN
The storage buffer is fixed at its initial size.
Attempting to extend the sbuf beyond this size results in an overflow condition.
.It Dv SBUF_AUTOEXTEND
This indicates that the storage buffer may be extended as necessary, so long
as resources allow, to hold additional data.
.El
.Pp
Note that if
.Fa buf
is not
.Dv NULL ,
it must point to an array of at least
.Fa length
characters.
The result of accessing that array directly while it is in use by the
sbuf is undefined.
.Pp
The
.Fn sbuf_delete
function clears the
.Fa sbuf
and frees any memory allocated for it.
There must be a call to
.Fn sbuf_delete
for every call to
.Fn sbuf_new .
Any attempt to access the sbuf after it has been deleted will fail.
.Pp
The
.Fn sbuf_clear
function invalidates the contents of the
.Fa sbuf
and resets its position to zero.
.Pp
The
.Fn sbuf_setpos
function sets the
.Fa sbuf Ns 's
end position to
.Fa 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.
.Pp
The
.Fn sbuf_bcat
function appends the first
.Fa len
bytes from the buffer
.Fa buf
to the
.Fa sbuf .
.Pp
The
.Fn sbuf_bcopyin
function copies
.Fa len
bytes from the specified userland address into the
.Fa sbuf .
.Pp
The
.Fn sbuf_bcpy
function replaces the contents of the
.Fa sbuf
with the first
.Fa len
bytes from the buffer
.Fa buf .
.Pp
The
.Fn sbuf_cat
function appends the NUL-terminated string
.Fa str
to the
.Fa sbuf
at the current position.
.Pp
The
.Fn sbuf_copyin
function copies a NUL-terminated string from the specified userland
address into the
.Fa sbuf .
If the
.Fa len
argument is non-zero, no more than
.Fa len
characters (not counting the terminating NUL) are copied; otherwise
the entire string, or as much of it as can fit in the
.Fa sbuf ,
is copied.
.Pp
The
.Fn sbuf_cpy
function replaces the contents of the
.Fa sbuf
with those of the NUL-terminated string
.Fa str .
This is equivalent to calling
.Fn sbuf_cat
with a fresh
.Fa sbuf
or one which position has been reset to zero with
.Fn sbuf_clear
or
.Fn sbuf_setpos .
.Pp
The
.Fn sbuf_printf
function formats its arguments according to the format string pointed
to by
.Fa fmt
and appends the resulting string to the
.Fa sbuf
at the current position.
.Pp
The
.Fn sbuf_vprintf
function behaves the same as
.Fn sbuf_printf
except that the arguments are obtained from the variable-length argument list
.Fa ap .
.Pp
The
.Fn sbuf_putc
function appends the character
.Fa c
to the
.Fa sbuf
at the current position.
.Pp
The
.Fn sbuf_trim
function removes trailing whitespace from the
.Fa sbuf .
.Pp
The
.Fn sbuf_overflowed
function returns a non-zero value if the
.Fa sbuf
overflowed.
.Pp
The
.Fn sbuf_finish
function null-terminates the
.Fa sbuf
and marks it as finished, which means that it may no longer be
modified using
.Fn sbuf_setpos ,
.Fn sbuf_cat ,
.Fn sbuf_cpy ,
.Fn sbuf_printf
or
.Fn sbuf_putc .
.Pp
The
.Fn sbuf_data
and
.Fn sbuf_len
functions return the actual string and its length, respectively;
.Fn sbuf_data
only works on a finished
.Fa sbuf .
.Fn sbuf_done
returns non-zero if the sbuf is finished.
.Sh NOTES
If an operation caused an
.Fa sbuf
to overflow, most subsequent operations on it will fail until the
.Fa sbuf
is finished using
.Fn sbuf_finish
or reset using
.Fn sbuf_clear ,
or its position is reset to a value between 0 and one less than the
size of its storage buffer using
.Fn sbuf_setpos ,
or it is reinitialized to a sufficiently short string using
.Fn sbuf_cpy .
.Sh RETURN VALUES
The
.Fn sbuf_new
function returns
.Dv NULL
if it failed to allocate a storage buffer, and a pointer to the new
.Fa sbuf
otherwise.
.Pp
The
.Fn sbuf_setpos
function returns \-1 if
.Fa pos
was invalid, and zero otherwise.
.Pp
The
.Fn sbuf_cat ,
.Fn sbuf_cpy ,
.Fn sbuf_printf ,
.Fn sbuf_putc ,
and
.Fn sbuf_trim
functions
all return \-1 if the buffer overflowed, and zero otherwise.
.Pp
The
.Fn sbuf_overflowed
function
returns a non-zero value if the buffer overflowed, and zero otherwise.
.Pp
The
.Fn sbuf_data
and
.Fn sbuf_len
functions return
.Dv NULL
and \-1, respectively, if the buffer overflowed.
.Pp
The
.Fn sbuf_copyin
function
returns \-1 if copying string from userland failed, and number of bytes
copied otherwise.
.Sh SEE ALSO
.Xr printf 3 ,
.Xr strcat 3 ,
.Xr strcpy 3 ,
.Xr copyin 9 ,
.Xr copyinstr 9 ,
.Xr printf 9
.Sh HISTORY
The
.Nm
family of functions first appeared in
.Fx 4.4 .
.Sh AUTHORS
.An -nosplit
The
.Nm
family of functions was designed by
.An Poul-Henning Kamp Aq phk@FreeBSD.org
and implemented by
.An Dag-Erling Sm\(/orgrav Aq des@FreeBSD.org .
Additional improvements were suggested by
.An Justin T. Gibbs Aq gibbs@FreeBSD.org .
Auto-extend support added by
.An Kelly Yancey Aq kbyanc@FreeBSD.org .
.Pp
This manual page was written by
.An Dag-Erling Sm\(/orgrav Aq des@FreeBSD.org .