16  * write-buffering support. Write buffers help to save space which otherwise
18  * Instead, data first goes to the write-buffer and is flushed when the
22  * UBIFS distinguishes between minimum write size (@c->min_io_size) and maximum
23  * write size (@c->max_write_size). The latter is the maximum amount of bytes
26  * @c->min_io_size <= @c->max_write_size. Write-buffers are of
28  * write-buffer is flushed, only the portion of it (aligned to @c->min_io_size
29  * boundary) which contains data is written, not the whole write-buffer,
33  * hand, we want to write in optimal @c->max_write_size bytes chunks, which
35  * other hand, we do not want to waste space when synchronizing the write
37  * the next write offset to be not aligned to @c->max_write_size bytes. So the
38  * have to make sure that the write-buffer offset (@wbuf->offs) becomes aligned
40  * write-buffer size (@wbuf->size).
42  * Write-buffers are defined by 'struct ubifs_wbuf' objects and protected by
44  * has to lock the write-buffer (e.g. journal space reservation code), many
45  * functions related to write-buffers have "nolock" suffix which means that the
46  * caller has to lock the write-buffer before calling this function.
296  * The flash media obliges us to write only in chunks of %c->min_io_size and
297  * when we have to write less data we add padding node to the write-buffer and
300  * padding node which takes %UBIFS_PAD_NODE_SZ bytes, we write padding bytes
469  * wbuf_timer_callback - write-buffer timer callback function.
470  * @timer: timer data (write-buffer descriptor)
472  * This function is called when the write-buffer timer expires.
486  * new_wbuf_timer - start new write-buffer timer.
488  * @wbuf: write-buffer descriptor
512  * cancel_wbuf_timer - cancel write-buffer timer.
513  * @wbuf: write-buffer descriptor
524  * ubifs_wbuf_sync_nolock - synchronize write-buffer.
525  * @wbuf: write-buffer to synchronize
527  * This function synchronizes write-buffer @buf and returns zero in case of
530  * Note, although write-buffers are of @c->max_write_size, this function does
532  * if the write-buffer is only partially filled with data, only the used part
533  * of the write-buffer (aligned on @c->min_io_size boundary) is synchronized.
543 		/* Write-buffer is empty or not seeked */  in ubifs_wbuf_sync_nolock()
561 	 * Do not write whole write buffer but write only the minimum necessary  in ubifs_wbuf_sync_nolock()
576 	 * But our goal is to optimize writes and make sure we write in  in ubifs_wbuf_sync_nolock()
581 	 * write-buffer flush we are again at the optimal offset (aligned to  in ubifs_wbuf_sync_nolock()
602  * ubifs_wbuf_seek_nolock - seek write-buffer.
603  * @wbuf: write-buffer
607  * This function targets the write-buffer to logical eraseblock @lnum:@offs.
608  * The write-buffer has to be empty. Returns zero in case of success and a
639  * ubifs_bg_wbufs_sync - synchronize write-buffers.
642  * This function is called by background thread to synchronize write-buffers.
682 			ubifs_err(c, "cannot sync write-buffer, error %d", err);  in ubifs_bg_wbufs_sync()
703  * ubifs_wbuf_write_nolock - write data to flash via write-buffer.
704  * @wbuf: write-buffer
705  * @buf: node to write
708  * This function writes data to flash via write-buffer @wbuf. This means that
710  * does not take whole max. write unit (@c->max_write_size). Instead, the node
711  * will sit in RAM until the write-buffer is synchronized (e.g., by timer, or
712  * because more data are appended to the write-buffer).
752 		 * write-buffer.  in ubifs_wbuf_write_nolock()
790 		 * write-buffer and switch to the next max. write unit.  in ubifs_wbuf_write_nolock()
806 		 * The write-buffer offset is not aligned to  in ubifs_wbuf_write_nolock()
808 		 * @c->max_write_size. Write @wbuf->size bytes to make sure the  in ubifs_wbuf_write_nolock()
812 		dbg_io("write %d bytes to LEB %d:%d",  in ubifs_wbuf_write_nolock()
826 	 * The remaining data may take more whole max. write units, so write the  in ubifs_wbuf_write_nolock()
827 	 * remains multiple to max. write unit size directly to the flash media.  in ubifs_wbuf_write_nolock()
834 		dbg_io("write %d bytes to LEB %d:%d", n, wbuf->lnum,  in ubifs_wbuf_write_nolock()
850 		 * max. write unit, so write it to the write-buffer and we are  in ubifs_wbuf_write_nolock()
879 	ubifs_err(c, "cannot write %d bytes to LEB %d:%d, error %d",  in ubifs_wbuf_write_nolock()
888  * ubifs_write_node_hmac - write node to the media.
890  * @buf: the node to write
930  * ubifs_write_node - write node to the media.
932  * @buf: the node to write
950  * ubifs_read_node_wbuf - read node from the media or write-buffer.
959  * in @buf. If the node partially or fully sits in the write-buffer, this
980 		/* We may safely unlock the write-buffer and read the data */  in ubifs_read_node_wbuf()
990 	/* Copy the rest from the write-buffer */  in ubifs_read_node_wbuf()
995 		/* Read everything that goes before write-buffer */  in ubifs_read_node_wbuf()
1088  * ubifs_wbuf_init - initialize write-buffer.
1090  * @wbuf: write-buffer to initialize
1092  * This function initializes write-buffer. Returns zero in case of success
1114 	 * If the LEB starts at the max. write size aligned address, then  in ubifs_wbuf_init()
1115 	 * write-buffer size has to be set to @c->max_write_size. Otherwise,  in ubifs_wbuf_init()
1117 	 * write size boundary.  in ubifs_wbuf_init()
1134  * @wbuf: the write-buffer where to add
1137  * This function adds an inode number to the inode array of the write-buffer.
1153  * @wbuf: the write-buffer
1156  * This function returns with %1 if the write-buffer contains some data from the
1175  * ubifs_sync_wbufs_by_inode - synchronize write-buffers for an inode.
1179  * This function synchronizes write-buffers which contain nodes belonging to