2 * UCW Library -- Fast Buffered I/O
4 * (c) 1997--2008 Martin Mares <mj@ucw.cz>
5 * (c) 2004 Robert Spalek <robert@ucw.cz>
7 * This software may be freely distributed and used according to the terms
8 * of the GNU Lesser General Public License.
11 #ifndef _UCW_FASTBUF_H
12 #define _UCW_FASTBUF_H
18 * === Internal structure [[internal]]
20 * Generally speaking, a fastbuf consists of a buffer and a set of callbacks.
21 * All front-end functions operate on the buffer and if the buffer becomes
22 * empty or fills up, they ask the corresponding callback to handle the
23 * situation. Back-ends then differ just in the definition of the callbacks.
25 * The state of the fastbuf is represented by a <<struct_fastbuf,`struct fastbuf`>>,
26 * which is a simple structure describing the state of the buffer (the pointers
27 * `buffer`, `bufend`), the front-end cursor (`bptr`), the back-end cursor (`bstop`),
28 * position of the back-end cursor in the file (`pos`), some flags (`flags`)
29 * and pointers to the callback functions.
31 * The buffer can be in one of the following states:
35 * +------------------------------------+---------------------------+
36 * | unused | free space |
37 * +------------------------------------+---------------------------+
39 * buffer <= bstop (BE pos) <= bptr (FE pos) <= bufend
41 * * This schema describes a fastbuf after its initialization or bflush().
42 * * There is no cached data and we are ready for any read or write operation
43 * (well, only if the back-end supports it).
44 * * The interval `[bptr, bufend]` can be used by front-ends
45 * for writing. If it is empty, the `spout` callback gets called
46 * upon the first write attempt to allocate a new buffer. Otherwise
47 * the fastbuf silently comes to the writing mode.
48 * * When a front-end needs to read something, it calls the `refill` callback.
49 * * The pointers can be either all non-`NULL` or all NULL.
50 * * `bstop == bptr` in most back-ends, but it is not necessary. Some
51 * in-memory streams take advantage of this.
55 * +------------------------------------+---------------------------+
56 * | read data | unused |
57 * +------------------------------------+---------------------------+
59 * buffer <= bptr (FE pos) <= bstop (BE pos) <= bufend
61 * * If we try to read something, we get to the reading mode.
62 * * No writing is allowed until a flush operation. But note that @bflush()
63 * will simply set `bptr` to `bstop` before `spout`
64 * and it breaks the position of the front-end's cursor,
65 * so the user should seek afwards.
66 * * The interval `[buffer, bstop]` contains a block of data read by the back-end.
67 * `bptr` is the front-end's cursor which points to the next character to be read.
68 * After the last character is read, `bptr == bstop` and the `refill` callback
69 * gets called upon the next read attempt to bring further data.
70 * This gives us an easy way how to implement @bungetc().
74 * +-----------------------+----------------+-----------------------+
75 * | unused | written data | free space |
76 * +-----------------------+----------------+-----------------------+
78 * buffer <= bstop (BE pos) < bptr (FE pos) <= bufend
80 * * This schema corresponds to the situation after a write attempt.
81 * * No reading is allowed until a flush operation.
82 * * The `bptr` points at the position where the next character
83 * will be written to. When we want to write, but `bptr == bufend`, we call
84 * the `spout` hook to flush the witten data and get an empty buffer.
85 * * `bstop` usually points at the beginning of the written data,
86 * but it is not necessary.
89 * Rules for back-ends:
91 * - Front-ends are only allowed to change the value of `bptr`, some flags
92 * and if a fatal error occurs, then also `bstop`. Back-ends can rely on it.
93 * - `buffer <= bstop <= bufend` and `buffer <= bptr <= bufend`.
94 * - `pos` should be the real position in the file corresponding to the location of `bstop` in the buffer.
95 * It can be modified by any back-end's callback, but the position of `bptr` (`pos + (bptr - bstop)`)
96 * must stay unchanged after `refill` or `spout`.
97 * - Failed callbacks (except `close`) should use @bthrow().
98 * - Any callback pointer may be NULL in case the callback is not implemented.
99 * - Callbacks can change not only `bptr` and `bstop`, but also the location and size of the buffer;
100 * the fb-mem back-end takes advantage of it.
103 * * out: `buffer <= bstop <= bptr <= bufend` (flushed).
106 * * in: `buffer <= bstop <= bptr <= bufend` (reading or flushed).
107 * * out: `buffer <= bptr <= bstop <= bufend` (reading).
108 * * Resulting `bptr == bstop` signals the end of file.
109 * The next reading attempt will again call `refill` which can succeed this time.
110 * * The callback must also return zero on EOF (iff `bptr == bstop`).
113 * * in: `buffer <= bstop <= bptr <= bufend` (writing or flushed).
114 * * out: `buffer <= bstop <= bptr < bufend` (flushed).
117 * * in: `buffer <= bstop <= bptr <= bufend` (flushed).
118 * * in: `(ofs >= 0 && whence == SEEK_SET) || (ofs <= 0 && whence == SEEK_END)`.
119 * * out: `buffer <= bstop <= bptr <= bufend` (flushed).
122 * * in: `buffer <= bstop <= bptr <= bufend` (flushed or after @bthrow()).
123 * * `close` must always free all internal structures, even when it throws an exception.
127 * This structure contains the state of the fastbuf. See the discussion above
131 byte is_fastbuf[0]; /* Dummy field for checking of type casts */
132 byte *bptr, *bstop; /* State of the buffer */
133 byte *buffer, *bufend; /* Start and end of the buffer */
134 char *name; /* File name (used for error messages) */
135 ucw_off_t pos; /* Position of bstop in the file */
136 int (*refill)(struct fastbuf *); /* Get a buffer with new data, returns 0 on EOF */
137 void (*spout)(struct fastbuf *); /* Write buffer data to the file */
138 int (*seek)(struct fastbuf *, ucw_off_t, int);/* Slow path for @bseek(), buffer already flushed; returns success */
139 void (*close)(struct fastbuf *); /* Close the stream */
140 int (*config)(struct fastbuf *, uns, int); /* Configure the stream */
141 int can_overwrite_buffer; /* Can the buffer be altered? 0=never, 1=temporarily, 2=permanently */
142 struct resource *res; /* The fastbuf can be tied to a resource pool */
145 void fb_tie(struct fastbuf *b); /* Tie fastbuf to a resource if there is an active pool */
148 * === Fastbuf on files [[fbparam]]
150 * If you want to use fastbufs to access files, you can choose one of several
151 * back-ends and set their parameters.
153 * All file fastbufs are tied to resources automatically.
160 FB_STD, /* Standard buffered I/O */
161 FB_DIRECT, /* Direct I/O bypassing system caches (see fb-direct.c for a description) */
162 FB_MMAP /* Memory mapped files */
166 * When you open a file fastbuf, you can use this structure to select a back-end
167 * and set its parameters. If you want just an "ordinary" file stream, you can
168 * happily pass NULL instead and the defaults from the configuration file (or
169 * hard-wired defaults if no config file has been read) will be used.
172 enum fb_type type; /* The chosen back-end */
173 uns buffer_size; /* 0 for default size */
174 uns keep_back_buf; /* FB_STD: optimize for bi-directional access */
175 uns read_ahead; /* FB_DIRECT options */
177 struct asio_queue *asio;
181 extern struct cf_section fbpar_cf; /** Configuration section with which you can fill the `fb_params` **/
182 extern struct fb_params fbpar_def; /** The default `fb_params` **/
185 * Opens a file with file mode @mode (see the man page of open()).
186 * Use @params to select the fastbuf back-end and its parameters or
187 * pass NULL if you are fine with defaults.
189 * Dies if the file does not exist.
191 struct fastbuf *bopen_file(const char *name, int mode, struct fb_params *params);
192 struct fastbuf *bopen_file_try(const char *name, int mode, struct fb_params *params); /** Like bopen_file(), but returns NULL on failure. **/
195 * Opens a temporary file.
196 * It is placed with other temp files and it is deleted when closed.
197 * Again, use NULL for @params if you want the defaults.
199 struct fastbuf *bopen_tmp_file(struct fb_params *params);
202 * Creates a fastbuf from a file descriptor @fd and sets its filename
203 * to @name (the name is used only in error messages).
204 * When the fastbuf is closed, the fd is closed as well. You can override
205 * this behavior by calling @bconfig().
207 struct fastbuf *bopen_fd_name(int fd, struct fb_params *params, const char *name);
208 static inline struct fastbuf *bopen_fd(int fd, struct fb_params *params) /** Same as above, but with an auto-generated filename. **/
210 return bopen_fd_name(fd, params, NULL);
214 * Flushes all buffers and makes sure that they are written to the disk.
216 void bfilesync(struct fastbuf *b);
219 * === Fastbufs on regular files [[fbfile]]
221 * If you want to use the `FB_STD` back-end and not worry about setting
222 * up any parameters, there is a couple of shortcuts.
225 struct fastbuf *bopen(const char *name, uns mode, uns buflen); /** Equivalent to @bopen_file() with `FB_STD` back-end. **/
226 struct fastbuf *bopen_try(const char *name, uns mode, uns buflen); /** Equivalent to @bopen_file_try() with `FB_STD` back-end. **/
227 struct fastbuf *bopen_tmp(uns buflen); /** Equivalent to @bopen_tmp_file() with `FB_STD` back-end. **/
228 struct fastbuf *bfdopen(int fd, uns buflen); /** Equivalent to @bopen_fd() with `FB_STD` back-end. **/
229 struct fastbuf *bfdopen_shared(int fd, uns buflen); /** Like @bfdopen(), but it does not close the @fd on @bclose(). **/
232 * === Temporary files [[fbtemp]]
234 * Usually, @bopen_tmp_file() is the best way how to come to a temporary file.
235 * However, in some specific cases you can need more, so there is also a set
236 * of more general functions.
239 #define TEMP_FILE_NAME_LEN 256
242 * Generates a temporary filename and stores it to the @name_buf (of size
243 * at least * `TEMP_FILE_NAME_LEN`). If @open_flags are not NULL, flags that
244 * should be OR-ed with other flags to open() will be stored there.
246 * The location and style of temporary files is controlled by the configuration.
247 * By default, the system temp directory (`$TMPDIR` or `/tmp`) is used.
249 * If the location is a publicly writeable directory (like `/tmp`), the
250 * generated filename cannot be guaranteed to be unique, so @open_flags
251 * will include `O_EXCL` and you have to check the result of open() and
254 * This function is not specific to fastbufs, it can be used separately.
256 void temp_file_name(char *name_buf, int *open_flags);
259 * Opens a temporary file and returns its file descriptor.
260 * You specify the file @mode and @open_flags passed to open().
262 * If the @name_buf (of at last `TEMP_FILE_NAME_LEN` chars) is not NULL,
263 * the filename is also stored in it.
265 * This function is not specific to fastbufs, it can be used separately.
267 int open_tmp(char *name_buf, int open_flags, int mode);
270 * Sometimes, a file is created as temporary and then moved to a stable
271 * location. This function takes a fastbuf created by @bopen_tmp_file()
272 * or @bopen_tmp(), marks it as permanent, closes it and renames it to
275 * Please note that it assumes that the temporary file and the @name
276 * are on the same volume (otherwise, rename() fails), so you might
277 * want to configure a special location for the temporary files
280 void bfix_tmp_file(struct fastbuf *fb, const char *name);
282 /* Internal functions of some file back-ends */
284 struct fastbuf *bfdopen_internal(int fd, const char *name, uns buflen);
285 struct fastbuf *bfmmopen_internal(int fd, const char *name, uns mode);
287 #ifdef CONFIG_UCW_FB_DIRECT
288 extern uns fbdir_cheat;
290 struct fastbuf *fbdir_open_fd_internal(int fd, const char *name, struct asio_queue *io_queue, uns buffer_size, uns read_ahead, uns write_back);
293 void bclose_file_helper(struct fastbuf *f, int fd, int is_temp_file);
296 * === Fastbufs on file fragments [[fblim]]
298 * The `fblim` back-end reads from a file handle, but at most a given
299 * number of bytes. This is frequently used for reading from sockets.
301 * All such fastbufs are tied to resources automatically.
304 struct fastbuf *bopen_limited_fd(int fd, uns bufsize, uns limit); /** Create a fastbuf which reads at most @limit bytes from @fd. **/
307 * === Fastbufs on in-memory streams [[fbmem]]
309 * The `fbmem` back-end keeps the whole contents of the stream
310 * in memory (as a linked list of memory blocks, so address space
311 * fragmentation is avoided).
313 * First, you use @fbmem_create() to create the stream and the fastbuf
314 * used for writing to it. Then you can call @fbmem_clone_read() to get
315 * an arbitrary number of fastbuf for reading from the stream.
317 * All in-memory fastbufs are tied to resources automatically.
320 struct fastbuf *fbmem_create(uns blocksize); /** Create stream and return its writing fastbuf. **/
321 struct fastbuf *fbmem_clone_read(struct fastbuf *f); /** Given a writing fastbuf, create a new reading fastbuf. **/
324 * === Fastbufs on static buffers [[fbbuf]]
326 * The `fbbuf` back-end stores the stream in a given block of memory.
327 * This is useful for parsing and generating of complex data structures.
331 * Creates a read-only fastbuf that takes its data from a given buffer.
332 * The fastbuf structure is allocated by the caller and pointed to by @f.
333 * The @buffer and @size specify the location and size of the buffer.
335 * In some cases, the front-ends can take advantage of rewriting the contents
336 * of the buffer temporarily. In this case, set @can_overwrite as described
337 * in <<internal,Internals>>. If you do not care, keep @can_overwrite zero.
339 * It is not possible to close this fastbuf. This implies that no tying to
340 * resources takes place.
342 void fbbuf_init_read(struct fastbuf *f, byte *buffer, uns size, uns can_overwrite);
345 * Creates a write-only fastbuf which writes into a provided memory buffer.
346 * The fastbuf structure is allocated by the caller and pointed to by @f.
347 * An attempt to write behind the end of the buffer dies.
349 * Data are written directly into the buffer, so it is not necessary to call @bflush()
352 * It is not possible to close this fastbuf. This implies that no tying to
353 * resources takes place.
355 void fbbuf_init_write(struct fastbuf *f, byte *buffer, uns size);
357 static inline uns fbbuf_count_written(struct fastbuf *f) /** Calculates, how many bytes were already written into the buffer. **/
359 return f->bptr - f->bstop;
363 * === Fastbuf on recyclable growing buffers [[fbgrow]]
365 * The `fbgrow` back-end keeps the stream in a contiguous buffer stored in the
366 * main memory, but unlike <<fbmem,`fbmem`>>, the buffer does not have a fixed
367 * size and it is expanded to accomodate all data.
369 * At every moment, you can use `fastbuf->buffer` to gain access to the stream.
371 * All fastbufs of this type are tied to resources automatically.
374 struct fastbuf *fbgrow_create(unsigned basic_size); /** Create the growing buffer pre-allocated to @basic_size bytes. **/
375 void fbgrow_reset(struct fastbuf *b); /** Reset stream and prepare for writing. **/
376 void fbgrow_rewind(struct fastbuf *b); /** Prepare for reading (of already written data). **/
379 * === Fastbuf on memory pools [[fbpool]]
381 * The write-only `fbpool` back-end also keeps the stream in a contiguous
382 * buffer, but this time the buffer is allocated from within a memory pool.
386 struct fbpool { /** Structure for fastbufs & mempools. **/
392 * Initialize a new `fbpool`. The structure is allocated by the caller,
393 * so bclose() should not be called and no resource tying takes place.
395 void fbpool_init(struct fbpool *fb); /** Initialize a new mempool fastbuf. **/
397 * Start a new continuous block and prepare for writing (see <<mempool:mp_start()>>).
398 * Provide the memory pool you want to use for this block as @mp.
400 void fbpool_start(struct fbpool *fb, struct mempool *mp, uns init_size);
402 * Close the block and return the address of its start (see <<mempool:mp_end()>>).
403 * The length can be determined by calling <<mempool:mp_size(mp, ptr)>>.
405 void *fbpool_end(struct fbpool *fb);
408 * === Atomic files for multi-threaded programs [[fbatomic]]
410 * This fastbuf backend is designed for cases when several threads
411 * of a single program append records to a common file and while the
412 * record can mix in an arbitrary way, the bytes inside a single
413 * record must remain uninterrupted.
415 * In case of files with fixed record size, we just allocate the
416 * buffer to hold a whole number of records and take advantage
417 * of the atomicity of the write() system call.
419 * With variable-sized records, we need another solution: when
420 * writing a record, we keep the fastbuf in a locked state, which
421 * prevents buffer flushing (and if the buffer becomes full, we extend it),
422 * and we wait for an explicit commit operation which write()s the buffer
423 * if the free space in the buffer falls below the expected maximum record
426 * Please note that initialization of the clones is not thread-safe,
427 * so you have to serialize it yourself.
429 * The atomic fastbufs are tied to resources automatically.
434 struct fb_atomic_file *af;
435 byte *expected_max_bptr;
438 #define FB_ATOMIC(f) ((struct fb_atomic *)(f)->is_fastbuf)
441 * Open an atomic fastbuf.
442 * If @master is NULL, the file @name is opened. If it is non-null,
443 * a new clone of an existing atomic fastbuf is created.
445 * If the file has fixed record length, just set @record_len to it.
446 * Otherwise set @record_len to the expected maximum record length
447 * with a negative sign (you need not fit in this length, but as long
448 * as you do, the fastbuf is more efficient) and call @fbatomic_commit()
451 * You can specify @record_len, if it is known (for optimisations).
453 * The file is closed when all fastbufs using it are closed.
455 struct fastbuf *fbatomic_open(const char *name, struct fastbuf *master, uns bufsize, int record_len);
456 void fbatomic_internal_write(struct fastbuf *b);
459 * Declare that you have finished writing a record. This is required only
460 * if a fixed record size was not specified.
462 static inline void fbatomic_commit(struct fastbuf *b)
464 if (b->bptr >= ((struct fb_atomic *)b)->expected_max_bptr)
465 fbatomic_internal_write(b);
468 /*** === Configuring stream parameters [[bconfig]] ***/
470 enum bconfig_type { /** Parameters that could be configured. **/
471 BCONFIG_IS_TEMP_FILE, /* 0=normal file, 1=temporary file, 2=shared fd */
472 BCONFIG_KEEP_BACK_BUF, /* Optimize for bi-directional access */
475 int bconfig(struct fastbuf *f, uns type, int data); /** Configure a fastbuf. Returns previous value. **/
477 /*** === Universal functions working on all fastbuf's [[ffbasic]] ***/
480 * Close and free fastbuf.
481 * Can not be used for fastbufs not returned from function (initialized in a parameter, for example the one from `fbbuf_init_read`).
483 void bclose(struct fastbuf *f);
484 void bflush(struct fastbuf *f); /** Write data (if it makes any sense, do not use for in-memory buffers). **/
485 void bseek(struct fastbuf *f, ucw_off_t pos, int whence); /** Seek in the buffer. See `man fseek` for description of @whence. Only for seekable fastbufs. **/
486 void bsetpos(struct fastbuf *f, ucw_off_t pos); /** Set position to @pos bytes from beginning. Only for seekable fastbufs. **/
487 void brewind(struct fastbuf *f); /** Go to the beginning of the fastbuf. Only for seekable ones. **/
488 ucw_off_t bfilesize(struct fastbuf *f); /** How large is the file? -1 if not seekable. **/
490 static inline ucw_off_t btell(struct fastbuf *f) /** Where am I (from the beginning)? **/
492 return f->pos + (f->bptr - f->bstop);
495 int bgetc_slow(struct fastbuf *f);
496 static inline int bgetc(struct fastbuf *f) /** Return next character from the buffer. **/
498 return (f->bptr < f->bstop) ? (int) *f->bptr++ : bgetc_slow(f);
501 int bpeekc_slow(struct fastbuf *f);
502 static inline int bpeekc(struct fastbuf *f) /** Return next character from the buffer, but keep the current position. **/
504 return (f->bptr < f->bstop) ? (int) *f->bptr : bpeekc_slow(f);
507 static inline void bungetc(struct fastbuf *f) /** Return last read character back. Only one back is guaranteed to work. **/
512 void bputc_slow(struct fastbuf *f, uns c);
513 static inline void bputc(struct fastbuf *f, uns c) /** Write a single character. **/
515 if (f->bptr < f->bufend)
521 static inline uns bavailr(struct fastbuf *f) /** Return the length of the cached data to be read. Do not use directly. **/
523 return f->bstop - f->bptr;
526 static inline uns bavailw(struct fastbuf *f) /** Return the length of the buffer available for writing. Do not use directly. **/
528 return f->bufend - f->bptr;
531 uns bread_slow(struct fastbuf *f, void *b, uns l, uns check);
533 * Read at most @l bytes of data into @b.
534 * Returns number of bytes read.
535 * 0 means end of file.
537 static inline uns bread(struct fastbuf *f, void *b, uns l)
541 memcpy(b, f->bptr, l);
546 return bread_slow(f, b, l, 0);
550 * Reads exactly @l bytes of data into @b.
551 * If at the end of file, it returns 0.
552 * If there are data, but less than @l, it dies.
554 static inline uns breadb(struct fastbuf *f, void *b, uns l)
558 memcpy(b, f->bptr, l);
563 return bread_slow(f, b, l, 1);
566 void bwrite_slow(struct fastbuf *f, const void *b, uns l);
567 static inline void bwrite(struct fastbuf *f, const void *b, uns l) /** Writes buffer @b of length @l into fastbuf. **/
571 memcpy(f->bptr, b, l);
575 bwrite_slow(f, b, l);
579 * Reads a line into @b and strips trailing `\n`.
580 * Returns pointer to the terminating 0 or NULL on `EOF`.
581 * Dies if the line is longer than @l.
583 char *bgets(struct fastbuf *f, char *b, uns l);
584 char *bgets0(struct fastbuf *f, char *b, uns l); /** The same as @bgets(), but for 0-terminated strings. **/
586 * Returns either length of read string (excluding the terminator) or -1 if it is too long.
587 * In such cases exactly @l bytes are read.
589 int bgets_nodie(struct fastbuf *f, char *b, uns l);
594 * Read a string, strip the trailing `\n` and store it into growing buffer @b.
595 * Dies if the line is longer than @limit.
597 uns bgets_bb(struct fastbuf *f, struct bb_t *b, uns limit);
599 * Read a string, strip the trailing `\n` and store it into buffer allocated from a memory pool.
601 char *bgets_mp(struct fastbuf *f, struct mempool *mp);
603 struct bgets_stk_struct {
605 byte *old_buf, *cur_buf, *src;
606 uns old_len, cur_len, src_len;
608 void bgets_stk_init(struct bgets_stk_struct *s);
609 void bgets_stk_step(struct bgets_stk_struct *s);
612 * Read a string, strip the trailing `\n` and store it on the stack (allocated using alloca()).
614 #define bgets_stk(fb) \
615 ({ struct bgets_stk_struct _s; _s.f = (fb); for (bgets_stk_init(&_s); _s.cur_len; _s.cur_buf = alloca(_s.cur_len), bgets_stk_step(&_s)); _s.cur_buf; })
618 * Write a string, without 0 or `\n` at the end.
620 static inline void bputs(struct fastbuf *f, const char *b)
622 bwrite(f, b, strlen(b));
626 * Write string, including terminating 0.
628 static inline void bputs0(struct fastbuf *f, const char *b)
630 bwrite(f, b, strlen(b)+1);
634 * Write string and append a newline to the end.
636 static inline void bputsn(struct fastbuf *f, const char *b)
642 void bbcopy_slow(struct fastbuf *f, struct fastbuf *t, uns l);
644 * Copy @l bytes of data from fastbuf @f to fastbuf @t.
645 * `UINT_MAX` (`~0U`) means all data, even if more than `UINT_MAX` bytes remain.
647 static inline void bbcopy(struct fastbuf *f, struct fastbuf *t, uns l)
649 if (bavailr(f) >= l && bavailw(t) >= l)
651 memcpy(t->bptr, f->bptr, l);
656 bbcopy_slow(f, t, l);
659 int bskip_slow(struct fastbuf *f, uns len);
660 static inline int bskip(struct fastbuf *f, uns len) /** Skip @len bytes without reading them. **/
662 if (bavailr(f) >= len)
668 return bskip_slow(f, len);
671 /*** === Direct I/O on buffers ***/
674 * Begin direct reading from fastbuf's internal buffer to avoid unnecessary copying.
675 * The function returns a buffer @buf together with its length in bytes (zero means EOF)
676 * with cached data to be read.
678 * Some back-ends allow the user to modify the data in the returned buffer to avoid unnecessary.
679 * If the back-end allows such modifications, it can set `f->can_overwrite_buffer` accordingly:
681 * - 0 if no modification is allowed,
682 * - 1 if the user can modify the buffer on the condition that
683 * the modifications will be undone before calling the next
685 * - 2 if the user is allowed to overwrite the data in the buffer
686 * if @bdirect_read_commit_modified() is called afterwards.
687 * In this case, the back-end must be prepared for trimming
688 * of the buffer which is done by the commit function.
690 * The reading must be ended by @bdirect_read_commit() or @bdirect_read_commit_modified(),
691 * unless the user did not read or modify anything.
693 static inline uns bdirect_read_prepare(struct fastbuf *f, byte **buf)
695 if (f->bptr == f->bstop && !f->refill(f))
697 *buf = NULL; // This is not needed, but it helps to get rid of spurious warnings
705 * End direct reading started by @bdirect_read_prepare() and move the cursor at @pos.
706 * Data in the returned buffer must be same as after @bdirect_read_prepare() and
707 * @pos must point somewhere inside the buffer.
709 static inline void bdirect_read_commit(struct fastbuf *f, byte *pos)
715 * Similar to @bdirect_read_commit(), but accepts also modified data before @pos.
716 * Note that such modifications are supported only if `f->can_overwrite_buffer == 2`.
718 static inline void bdirect_read_commit_modified(struct fastbuf *f, byte *pos)
721 f->buffer = pos; /* Avoid seeking backwards in the buffer */
725 * Start direct writing to fastbuf's internal buffer to avoid copy overhead.
726 * The function returns the length of the buffer in @buf (at least one byte)
727 * where we can write to. The operation must be ended by @bdirect_write_commit(),
728 * unless nothing is written.
730 static inline uns bdirect_write_prepare(struct fastbuf *f, byte **buf)
732 if (f->bptr == f->bufend)
739 * Commit the data written to the buffer returned by @bdirect_write_prepare().
740 * The length is specified by @pos which must point just after the written data.
741 * Also moves the cursor to @pos.
743 static inline void bdirect_write_commit(struct fastbuf *f, byte *pos)
748 /*** === Formatted output ***/
751 * printf into a fastbuf.
753 int bprintf(struct fastbuf *b, const char *msg, ...)
754 FORMAT_CHECK(printf,2,3);
755 int vbprintf(struct fastbuf *b, const char *msg, va_list args); /** vprintf into a fastbuf. **/