sbuf_set_drain (9)

Leading comments

-
 Copyright (c) 2000 Poul-Henning Kamp and Dag-Erling Coïdan Smørgrav
 All rights reserved.

 Redistribution and use in source and binary forms, with or without
 modification, are permitted provided that the following conditions
 are met:
 1. Redistributions of source code must retain the above copyright
    notice, this list of conditions and the following disclaimer.
 2. Redistributions in binary form must reproduce the above copyright
    notice, this list of conditions and the following ...

(The comments found at the beginning of the groff file "man9/sbuf_set_drain.9freebsd".)

NAME

sbuf sbuf_new sbuf_new_auto sbuf_new_for_sysctl sbuf_clear 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 - safe string composition

SYNOPSIS

In sys/types.h In sys/sbuf.h Ft typedef int ( sbuf_drain_func ) ( void *arg, const char *data, int len ) ;

Ft struct sbuf * Fn sbuf_new struct sbuf *s char *buf int length int flags Ft struct sbuf * Fn sbuf_new_auto 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 void Fn sbuf_set_drain struct sbuf *s sbuf_drain_func *func void *arg Ft int Fn sbuf_trim struct sbuf *s Ft int Fn sbuf_error struct sbuf *s Ft int Fn sbuf_finish struct sbuf *s Ft char * Fn sbuf_data struct sbuf *s Ft ssize_t Fn sbuf_len struct sbuf *s Ft int Fn sbuf_done struct sbuf *s Ft void Fn sbuf_delete struct sbuf *s Ft void Fn sbuf_start_section struct sbuf *s ssize_t *old_lenp Ft ssize_t Fn sbuf_end_section struct sbuf *s ssize_t old_len size_t pad int c In sys/sysctl.h Ft struct sbuf * Fn sbuf_new_for_sysctl struct sbuf *s char *buf int length struct sysctl_req *req

DESCRIPTION

The ifconfig 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 Fa sbufs , defined in 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 Fn sbuf_new function initializes the Fa sbuf pointed to by its first argument. If that pointer is NULL Fn sbuf_new allocates a Vt struct sbuf using malloc(9). The Fa buf argument is a pointer to a buffer in which to store the actual string; if it is NULL Fn sbuf_new will allocate one using 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:

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.

Note that if Fa buf is not 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.

The Fn sbuf_new_auto function is a shortcut for creating a completely dynamic . It is the equivalent of calling Fn sbuf_new with values NULL NULL 0 and SBUF_AUTOEXTEND

The Fn sbuf_new_for_sysctl function will set up an sbuf with a drain function to use Fn 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 Fn sysctl_wire_old_buffer .

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.

The Fn sbuf_clear function invalidates the contents of the Fa sbuf and resets its position to zero.

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.

The Fn sbuf_bcat function appends the first Fa len bytes from the buffer Fa buf to the Fa sbuf .

The Fn sbuf_bcopyin function copies Fa len bytes from the specified userland address into the Fa sbuf .

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

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

The Fn sbuf_set_drain function sets a drain function Fa func for the Fa sbuf , and records a pointer Fa arg to be passed to the drain on callback. The drain function cannot be changed while Fa sbuf_len is non-zero.

The registered drain function Vt sbuf_drain_func will be called with the argument Fa arg provided to Fn sbuf_set_drain , a pointer Fa data to a byte string that is the contents of the sbuf, and the length Fa len of the data. If the drain function exists, it will be called when the sbuf internal buffer is full, or on behalf of Fn 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 Fn 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 Fn sbuf_bcopyin , Fn sbuf_copyin , Fn sbuf_trim , and Fn sbuf_data functions cannot be used on an sbuf with a drain.

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.

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 .

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.

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 .

The Fn sbuf_putc function appends the character Fa c to the Fa sbuf at the current position.

The Fn sbuf_trim function removes trailing whitespace from the Fa sbuf .

The Fn sbuf_error function returns any error value that the Fa sbuf may have accumulated, either from the drain function, or ENOMEM if the Fa sbuf overflowed. This function is generally not needed and instead the error code from Fn sbuf_finish is the preferred way to discover whether an sbuf had an error.

The Fn sbuf_finish function will call the attached drain function if one exists until all the data in the Fa sbuf is flushed. If there is no attached drain, Fn sbuf_finish NUL-terminates the Fa sbuf . In either case it marks the Fa sbuf 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 , until Fn sbuf_clear is used to reset the sbuf.

The Fn sbuf_data function returns the actual string; Fn sbuf_data only works on a finished Fa sbuf . The Fn sbuf_len function returns the length of the string. For an Fa sbuf with an attached drain, Fn sbuf_len returns the length of the un-drained data. Fn sbuf_done returns non-zero if the Fa sbuf is finished.

The Fn sbuf_start_section and Fn sbuf_end_section functions may be used for automatic section alignment. The arguments Fa pad and Fa c specify the padding size and a character used for padding. The arguments Fa old_lenp and Fa 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 Fa old_lenp and Fa old_len respectively.

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 .

Drains in user-space will not always function as indicated. While the drain function will be called immediately on overflow from the Fa sbuf_putc , Fa sbuf_bcat , Fa sbuf_cat functions, Fa sbuf_printf and Fa 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 Fn sbuf_new function returns NULL if it failed to allocate a storage buffer, and a pointer to the new Fa sbuf otherwise.

The Fn sbuf_setpos function returns -1 if Fa pos was invalid, and zero otherwise.

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.

The Fn sbuf_error function returns a non-zero value if the buffer has an overflow or drain error, and zero otherwise.

The Fn sbuf_len function returns -1 if the buffer overflowed.

The Fn sbuf_copyin function returns -1 if copying string from userland failed, and number of bytes copied otherwise.

The Fn sbuf_end_section function returns the section length or -1 if the buffer has an error.

The Fn 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 Fn sbuf_finish 3 function (the userland version) will return zero for success and -1 and set errno on error.

EXAMPLES

#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

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

HISTORY

The ifconfig family of functions first appeared in Fx 4.4 .

AUTHORS

An -nosplit The ifconfig 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 . Drain functionality added by An Matthew Fleming Aq mdf@FreeBSD.org .

This manual page was written by An Dag-Erling Sm/orgrav Aq des@FreeBSD.org .