2 * Copyright (C) 2008 Oracle. All rights reserved.
4 * This program is free software; you can redistribute it and/or
5 * modify it under the terms of the GNU General Public
6 * License v2 as published by the Free Software Foundation.
8 * This program is distributed in the hope that it will be useful,
9 * but WITHOUT ANY WARRANTY; without even the implied warranty of
10 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
11 * General Public License for more details.
13 * You should have received a copy of the GNU General Public
14 * License along with this program; if not, write to the
15 * Free Software Foundation, Inc., 59 Temple Place - Suite 330,
16 * Boston, MA 021110-1307, USA.
19 #include <linux/kernel.h>
20 #include <linux/bio.h>
21 #include <linux/buffer_head.h>
22 #include <linux/file.h>
24 #include <linux/pagemap.h>
25 #include <linux/highmem.h>
26 #include <linux/time.h>
27 #include <linux/init.h>
28 #include <linux/string.h>
29 #include <linux/backing-dev.h>
30 #include <linux/mpage.h>
31 #include <linux/swap.h>
32 #include <linux/writeback.h>
33 #include <linux/bit_spinlock.h>
34 #include <linux/slab.h>
38 #include "transaction.h"
39 #include "btrfs_inode.h"
41 #include "ordered-data.h"
42 #include "compression.h"
43 #include "extent_io.h"
44 #include "extent_map.h"
46 struct compressed_bio {
47 /* number of bios pending for this compressed extent */
48 atomic_t pending_bios;
50 /* the pages with the compressed data on them */
51 struct page **compressed_pages;
53 /* inode that owns this data */
56 /* starting offset in the inode for our pages */
59 /* number of bytes in the inode we're working on */
62 /* number of bytes on disk */
63 unsigned long compressed_len;
65 /* the compression algorithm for this bio */
68 /* number of compressed pages in the array */
69 unsigned long nr_pages;
75 /* for reads, this is the bio we are copying the data into */
79 * the start of a variable length array of checksums only
85 static inline int compressed_bio_size(struct btrfs_root *root,
86 unsigned long disk_size)
88 u16 csum_size = btrfs_super_csum_size(&root->fs_info->super_copy);
89 return sizeof(struct compressed_bio) +
90 ((disk_size + root->sectorsize - 1) / root->sectorsize) *
94 static struct bio *compressed_bio_alloc(struct block_device *bdev,
95 u64 first_byte, gfp_t gfp_flags)
99 nr_vecs = bio_get_nr_vecs(bdev);
100 return btrfs_bio_alloc(bdev, first_byte >> 9, nr_vecs, gfp_flags);
103 static int check_compressed_csum(struct inode *inode,
104 struct compressed_bio *cb,
108 struct btrfs_root *root = BTRFS_I(inode)->root;
113 u32 *cb_sum = &cb->sums;
115 if (BTRFS_I(inode)->flags & BTRFS_INODE_NODATASUM)
118 for (i = 0; i < cb->nr_pages; i++) {
119 page = cb->compressed_pages[i];
122 kaddr = kmap_atomic(page, KM_USER0);
123 csum = btrfs_csum_data(root, kaddr, csum, PAGE_CACHE_SIZE);
124 btrfs_csum_final(csum, (char *)&csum);
125 kunmap_atomic(kaddr, KM_USER0);
127 if (csum != *cb_sum) {
128 printk(KERN_INFO "btrfs csum failed ino %lu "
129 "extent %llu csum %u "
130 "wanted %u mirror %d\n", inode->i_ino,
131 (unsigned long long)disk_start,
132 csum, *cb_sum, cb->mirror_num);
144 /* when we finish reading compressed pages from the disk, we
145 * decompress them and then run the bio end_io routines on the
146 * decompressed pages (in the inode address space).
148 * This allows the checksumming and other IO error handling routines
151 * The compressed pages are freed here, and it must be run
154 static void end_compressed_bio_read(struct bio *bio, int err)
156 struct compressed_bio *cb = bio->bi_private;
165 /* if there are more bios still pending for this compressed
168 if (!atomic_dec_and_test(&cb->pending_bios))
172 ret = check_compressed_csum(inode, cb, (u64)bio->bi_sector << 9);
176 /* ok, we're the last bio for this extent, lets start
179 ret = btrfs_decompress_biovec(cb->compress_type,
180 cb->compressed_pages,
182 cb->orig_bio->bi_io_vec,
183 cb->orig_bio->bi_vcnt,
189 /* release the compressed pages */
191 for (index = 0; index < cb->nr_pages; index++) {
192 page = cb->compressed_pages[index];
193 page->mapping = NULL;
194 page_cache_release(page);
197 /* do io completion on the original bio */
199 bio_io_error(cb->orig_bio);
202 struct bio_vec *bvec = cb->orig_bio->bi_io_vec;
205 * we have verified the checksum already, set page
206 * checked so the end_io handlers know about it
208 while (bio_index < cb->orig_bio->bi_vcnt) {
209 SetPageChecked(bvec->bv_page);
213 bio_endio(cb->orig_bio, 0);
216 /* finally free the cb struct */
217 kfree(cb->compressed_pages);
224 * Clear the writeback bits on all of the file
225 * pages for a compressed write
227 static noinline int end_compressed_writeback(struct inode *inode, u64 start,
228 unsigned long ram_size)
230 unsigned long index = start >> PAGE_CACHE_SHIFT;
231 unsigned long end_index = (start + ram_size - 1) >> PAGE_CACHE_SHIFT;
232 struct page *pages[16];
233 unsigned long nr_pages = end_index - index + 1;
237 while (nr_pages > 0) {
238 ret = find_get_pages_contig(inode->i_mapping, index,
240 nr_pages, ARRAY_SIZE(pages)), pages);
246 for (i = 0; i < ret; i++) {
247 end_page_writeback(pages[i]);
248 page_cache_release(pages[i]);
253 /* the inode may be gone now */
258 * do the cleanup once all the compressed pages hit the disk.
259 * This will clear writeback on the file pages and free the compressed
262 * This also calls the writeback end hooks for the file pages so that
263 * metadata and checksums can be updated in the file.
265 static void end_compressed_bio_write(struct bio *bio, int err)
267 struct extent_io_tree *tree;
268 struct compressed_bio *cb = bio->bi_private;
276 /* if there are more bios still pending for this compressed
279 if (!atomic_dec_and_test(&cb->pending_bios))
282 /* ok, we're the last bio for this extent, step one is to
283 * call back into the FS and do all the end_io operations
286 tree = &BTRFS_I(inode)->io_tree;
287 cb->compressed_pages[0]->mapping = cb->inode->i_mapping;
288 tree->ops->writepage_end_io_hook(cb->compressed_pages[0],
290 cb->start + cb->len - 1,
292 cb->compressed_pages[0]->mapping = NULL;
294 end_compressed_writeback(inode, cb->start, cb->len);
295 /* note, our inode could be gone now */
298 * release the compressed pages, these came from alloc_page and
299 * are not attached to the inode at all
302 for (index = 0; index < cb->nr_pages; index++) {
303 page = cb->compressed_pages[index];
304 page->mapping = NULL;
305 page_cache_release(page);
308 /* finally free the cb struct */
309 kfree(cb->compressed_pages);
316 * worker function to build and submit bios for previously compressed pages.
317 * The corresponding pages in the inode should be marked for writeback
318 * and the compressed pages should have a reference on them for dropping
319 * when the IO is complete.
321 * This also checksums the file bytes and gets things ready for
324 int btrfs_submit_compressed_write(struct inode *inode, u64 start,
325 unsigned long len, u64 disk_start,
326 unsigned long compressed_len,
327 struct page **compressed_pages,
328 unsigned long nr_pages)
330 struct bio *bio = NULL;
331 struct btrfs_root *root = BTRFS_I(inode)->root;
332 struct compressed_bio *cb;
333 unsigned long bytes_left;
334 struct extent_io_tree *io_tree = &BTRFS_I(inode)->io_tree;
337 u64 first_byte = disk_start;
338 struct block_device *bdev;
341 WARN_ON(start & ((u64)PAGE_CACHE_SIZE - 1));
342 cb = kmalloc(compressed_bio_size(root, compressed_len), GFP_NOFS);
345 atomic_set(&cb->pending_bios, 0);
351 cb->compressed_pages = compressed_pages;
352 cb->compressed_len = compressed_len;
354 cb->nr_pages = nr_pages;
356 bdev = BTRFS_I(inode)->root->fs_info->fs_devices->latest_bdev;
358 bio = compressed_bio_alloc(bdev, first_byte, GFP_NOFS);
363 bio->bi_private = cb;
364 bio->bi_end_io = end_compressed_bio_write;
365 atomic_inc(&cb->pending_bios);
367 /* create and submit bios for the compressed pages */
368 bytes_left = compressed_len;
369 for (page_index = 0; page_index < cb->nr_pages; page_index++) {
370 page = compressed_pages[page_index];
371 page->mapping = inode->i_mapping;
373 ret = io_tree->ops->merge_bio_hook(page, 0,
379 page->mapping = NULL;
380 if (ret || bio_add_page(bio, page, PAGE_CACHE_SIZE, 0) <
385 * inc the count before we submit the bio so
386 * we know the end IO handler won't happen before
387 * we inc the count. Otherwise, the cb might get
388 * freed before we're done setting it up
390 atomic_inc(&cb->pending_bios);
391 ret = btrfs_bio_wq_end_io(root->fs_info, bio, 0);
394 ret = btrfs_csum_one_bio(root, inode, bio, start, 1);
397 ret = btrfs_map_bio(root, WRITE, bio, 0, 1);
402 bio = compressed_bio_alloc(bdev, first_byte, GFP_NOFS);
403 bio->bi_private = cb;
404 bio->bi_end_io = end_compressed_bio_write;
405 bio_add_page(bio, page, PAGE_CACHE_SIZE, 0);
407 if (bytes_left < PAGE_CACHE_SIZE) {
408 printk("bytes left %lu compress len %lu nr %lu\n",
409 bytes_left, cb->compressed_len, cb->nr_pages);
411 bytes_left -= PAGE_CACHE_SIZE;
412 first_byte += PAGE_CACHE_SIZE;
417 ret = btrfs_bio_wq_end_io(root->fs_info, bio, 0);
420 ret = btrfs_csum_one_bio(root, inode, bio, start, 1);
423 ret = btrfs_map_bio(root, WRITE, bio, 0, 1);
430 static noinline int add_ra_bio_pages(struct inode *inode,
432 struct compressed_bio *cb)
434 unsigned long end_index;
435 unsigned long page_index;
437 u64 isize = i_size_read(inode);
440 unsigned long nr_pages = 0;
441 struct extent_map *em;
442 struct address_space *mapping = inode->i_mapping;
443 struct extent_map_tree *em_tree;
444 struct extent_io_tree *tree;
448 page = cb->orig_bio->bi_io_vec[cb->orig_bio->bi_vcnt - 1].bv_page;
449 last_offset = (page_offset(page) + PAGE_CACHE_SIZE);
450 em_tree = &BTRFS_I(inode)->extent_tree;
451 tree = &BTRFS_I(inode)->io_tree;
456 end_index = (i_size_read(inode) - 1) >> PAGE_CACHE_SHIFT;
458 while (last_offset < compressed_end) {
459 page_index = last_offset >> PAGE_CACHE_SHIFT;
461 if (page_index > end_index)
465 page = radix_tree_lookup(&mapping->page_tree, page_index);
474 page = __page_cache_alloc(mapping_gfp_mask(mapping) &
479 if (add_to_page_cache_lru(page, mapping, page_index,
481 page_cache_release(page);
485 end = last_offset + PAGE_CACHE_SIZE - 1;
487 * at this point, we have a locked page in the page cache
488 * for these bytes in the file. But, we have to make
489 * sure they map to this compressed extent on disk.
491 set_page_extent_mapped(page);
492 lock_extent(tree, last_offset, end, GFP_NOFS);
493 read_lock(&em_tree->lock);
494 em = lookup_extent_mapping(em_tree, last_offset,
496 read_unlock(&em_tree->lock);
498 if (!em || last_offset < em->start ||
499 (last_offset + PAGE_CACHE_SIZE > extent_map_end(em)) ||
500 (em->block_start >> 9) != cb->orig_bio->bi_sector) {
502 unlock_extent(tree, last_offset, end, GFP_NOFS);
504 page_cache_release(page);
509 if (page->index == end_index) {
511 size_t zero_offset = isize & (PAGE_CACHE_SIZE - 1);
515 zeros = PAGE_CACHE_SIZE - zero_offset;
516 userpage = kmap_atomic(page, KM_USER0);
517 memset(userpage + zero_offset, 0, zeros);
518 flush_dcache_page(page);
519 kunmap_atomic(userpage, KM_USER0);
523 ret = bio_add_page(cb->orig_bio, page,
526 if (ret == PAGE_CACHE_SIZE) {
528 page_cache_release(page);
530 unlock_extent(tree, last_offset, end, GFP_NOFS);
532 page_cache_release(page);
536 last_offset += PAGE_CACHE_SIZE;
542 * for a compressed read, the bio we get passed has all the inode pages
543 * in it. We don't actually do IO on those pages but allocate new ones
544 * to hold the compressed pages on disk.
546 * bio->bi_sector points to the compressed extent on disk
547 * bio->bi_io_vec points to all of the inode pages
548 * bio->bi_vcnt is a count of pages
550 * After the compressed pages are read, we copy the bytes into the
551 * bio we were passed and then call the bio end_io calls
553 int btrfs_submit_compressed_read(struct inode *inode, struct bio *bio,
554 int mirror_num, unsigned long bio_flags)
556 struct extent_io_tree *tree;
557 struct extent_map_tree *em_tree;
558 struct compressed_bio *cb;
559 struct btrfs_root *root = BTRFS_I(inode)->root;
560 unsigned long uncompressed_len = bio->bi_vcnt * PAGE_CACHE_SIZE;
561 unsigned long compressed_len;
562 unsigned long nr_pages;
563 unsigned long page_index;
565 struct block_device *bdev;
566 struct bio *comp_bio;
567 u64 cur_disk_byte = (u64)bio->bi_sector << 9;
570 struct extent_map *em;
574 tree = &BTRFS_I(inode)->io_tree;
575 em_tree = &BTRFS_I(inode)->extent_tree;
577 /* we need the actual starting offset of this extent in the file */
578 read_lock(&em_tree->lock);
579 em = lookup_extent_mapping(em_tree,
580 page_offset(bio->bi_io_vec->bv_page),
582 read_unlock(&em_tree->lock);
584 compressed_len = em->block_len;
585 cb = kmalloc(compressed_bio_size(root, compressed_len), GFP_NOFS);
589 atomic_set(&cb->pending_bios, 0);
592 cb->mirror_num = mirror_num;
595 cb->start = em->orig_start;
597 em_start = em->start;
602 cb->len = uncompressed_len;
603 cb->compressed_len = compressed_len;
604 cb->compress_type = extent_compress_type(bio_flags);
607 nr_pages = (compressed_len + PAGE_CACHE_SIZE - 1) /
609 cb->compressed_pages = kzalloc(sizeof(struct page *) * nr_pages,
611 if (!cb->compressed_pages)
614 bdev = BTRFS_I(inode)->root->fs_info->fs_devices->latest_bdev;
616 for (page_index = 0; page_index < nr_pages; page_index++) {
617 cb->compressed_pages[page_index] = alloc_page(GFP_NOFS |
619 if (!cb->compressed_pages[page_index])
622 cb->nr_pages = nr_pages;
624 add_ra_bio_pages(inode, em_start + em_len, cb);
626 /* include any pages we added in add_ra-bio_pages */
627 uncompressed_len = bio->bi_vcnt * PAGE_CACHE_SIZE;
628 cb->len = uncompressed_len;
630 comp_bio = compressed_bio_alloc(bdev, cur_disk_byte, GFP_NOFS);
633 comp_bio->bi_private = cb;
634 comp_bio->bi_end_io = end_compressed_bio_read;
635 atomic_inc(&cb->pending_bios);
637 for (page_index = 0; page_index < nr_pages; page_index++) {
638 page = cb->compressed_pages[page_index];
639 page->mapping = inode->i_mapping;
640 page->index = em_start >> PAGE_CACHE_SHIFT;
642 if (comp_bio->bi_size)
643 ret = tree->ops->merge_bio_hook(page, 0,
649 page->mapping = NULL;
650 if (ret || bio_add_page(comp_bio, page, PAGE_CACHE_SIZE, 0) <
654 ret = btrfs_bio_wq_end_io(root->fs_info, comp_bio, 0);
658 * inc the count before we submit the bio so
659 * we know the end IO handler won't happen before
660 * we inc the count. Otherwise, the cb might get
661 * freed before we're done setting it up
663 atomic_inc(&cb->pending_bios);
665 if (!(BTRFS_I(inode)->flags & BTRFS_INODE_NODATASUM)) {
666 ret = btrfs_lookup_bio_sums(root, inode,
670 sums += (comp_bio->bi_size + root->sectorsize - 1) /
673 ret = btrfs_map_bio(root, READ, comp_bio,
679 comp_bio = compressed_bio_alloc(bdev, cur_disk_byte,
681 comp_bio->bi_private = cb;
682 comp_bio->bi_end_io = end_compressed_bio_read;
684 bio_add_page(comp_bio, page, PAGE_CACHE_SIZE, 0);
686 cur_disk_byte += PAGE_CACHE_SIZE;
690 ret = btrfs_bio_wq_end_io(root->fs_info, comp_bio, 0);
693 if (!(BTRFS_I(inode)->flags & BTRFS_INODE_NODATASUM)) {
694 ret = btrfs_lookup_bio_sums(root, inode, comp_bio, sums);
698 ret = btrfs_map_bio(root, READ, comp_bio, mirror_num, 0);
705 for (page_index = 0; page_index < nr_pages; page_index++)
706 free_page((unsigned long)cb->compressed_pages[page_index]);
708 kfree(cb->compressed_pages);
716 static struct list_head comp_idle_workspace[BTRFS_COMPRESS_TYPES];
717 static spinlock_t comp_workspace_lock[BTRFS_COMPRESS_TYPES];
718 static int comp_num_workspace[BTRFS_COMPRESS_TYPES];
719 static atomic_t comp_alloc_workspace[BTRFS_COMPRESS_TYPES];
720 static wait_queue_head_t comp_workspace_wait[BTRFS_COMPRESS_TYPES];
722 struct btrfs_compress_op *btrfs_compress_op[] = {
723 &btrfs_zlib_compress,
727 int __init btrfs_init_compress(void)
731 for (i = 0; i < BTRFS_COMPRESS_TYPES; i++) {
732 INIT_LIST_HEAD(&comp_idle_workspace[i]);
733 spin_lock_init(&comp_workspace_lock[i]);
734 atomic_set(&comp_alloc_workspace[i], 0);
735 init_waitqueue_head(&comp_workspace_wait[i]);
741 * this finds an available workspace or allocates a new one
742 * ERR_PTR is returned if things go bad.
744 static struct list_head *find_workspace(int type)
746 struct list_head *workspace;
747 int cpus = num_online_cpus();
750 struct list_head *idle_workspace = &comp_idle_workspace[idx];
751 spinlock_t *workspace_lock = &comp_workspace_lock[idx];
752 atomic_t *alloc_workspace = &comp_alloc_workspace[idx];
753 wait_queue_head_t *workspace_wait = &comp_workspace_wait[idx];
754 int *num_workspace = &comp_num_workspace[idx];
756 spin_lock(workspace_lock);
757 if (!list_empty(idle_workspace)) {
758 workspace = idle_workspace->next;
761 spin_unlock(workspace_lock);
765 if (atomic_read(alloc_workspace) > cpus) {
768 spin_unlock(workspace_lock);
769 prepare_to_wait(workspace_wait, &wait, TASK_UNINTERRUPTIBLE);
770 if (atomic_read(alloc_workspace) > cpus && !*num_workspace)
772 finish_wait(workspace_wait, &wait);
775 atomic_inc(alloc_workspace);
776 spin_unlock(workspace_lock);
778 workspace = btrfs_compress_op[idx]->alloc_workspace();
779 if (IS_ERR(workspace)) {
780 atomic_dec(alloc_workspace);
781 wake_up(workspace_wait);
787 * put a workspace struct back on the list or free it if we have enough
788 * idle ones sitting around
790 static void free_workspace(int type, struct list_head *workspace)
793 struct list_head *idle_workspace = &comp_idle_workspace[idx];
794 spinlock_t *workspace_lock = &comp_workspace_lock[idx];
795 atomic_t *alloc_workspace = &comp_alloc_workspace[idx];
796 wait_queue_head_t *workspace_wait = &comp_workspace_wait[idx];
797 int *num_workspace = &comp_num_workspace[idx];
799 spin_lock(workspace_lock);
800 if (*num_workspace < num_online_cpus()) {
801 list_add_tail(workspace, idle_workspace);
803 spin_unlock(workspace_lock);
806 spin_unlock(workspace_lock);
808 btrfs_compress_op[idx]->free_workspace(workspace);
809 atomic_dec(alloc_workspace);
811 if (waitqueue_active(workspace_wait))
812 wake_up(workspace_wait);
816 * cleanup function for module exit
818 static void free_workspaces(void)
820 struct list_head *workspace;
823 for (i = 0; i < BTRFS_COMPRESS_TYPES; i++) {
824 while (!list_empty(&comp_idle_workspace[i])) {
825 workspace = comp_idle_workspace[i].next;
827 btrfs_compress_op[i]->free_workspace(workspace);
828 atomic_dec(&comp_alloc_workspace[i]);
834 * given an address space and start/len, compress the bytes.
836 * pages are allocated to hold the compressed result and stored
839 * out_pages is used to return the number of pages allocated. There
840 * may be pages allocated even if we return an error
842 * total_in is used to return the number of bytes actually read. It
843 * may be smaller then len if we had to exit early because we
844 * ran out of room in the pages array or because we cross the
847 * total_out is used to return the total number of compressed bytes
849 * max_out tells us the max number of bytes that we're allowed to
852 int btrfs_compress_pages(int type, struct address_space *mapping,
853 u64 start, unsigned long len,
855 unsigned long nr_dest_pages,
856 unsigned long *out_pages,
857 unsigned long *total_in,
858 unsigned long *total_out,
859 unsigned long max_out)
861 struct list_head *workspace;
864 workspace = find_workspace(type);
865 if (IS_ERR(workspace))
868 ret = btrfs_compress_op[type-1]->compress_pages(workspace, mapping,
870 nr_dest_pages, out_pages,
873 free_workspace(type, workspace);
878 * pages_in is an array of pages with compressed data.
880 * disk_start is the starting logical offset of this array in the file
882 * bvec is a bio_vec of pages from the file that we want to decompress into
884 * vcnt is the count of pages in the biovec
886 * srclen is the number of bytes in pages_in
888 * The basic idea is that we have a bio that was created by readpages.
889 * The pages in the bio are for the uncompressed data, and they may not
890 * be contiguous. They all correspond to the range of bytes covered by
891 * the compressed extent.
893 int btrfs_decompress_biovec(int type, struct page **pages_in, u64 disk_start,
894 struct bio_vec *bvec, int vcnt, size_t srclen)
896 struct list_head *workspace;
899 workspace = find_workspace(type);
900 if (IS_ERR(workspace))
903 ret = btrfs_compress_op[type-1]->decompress_biovec(workspace, pages_in,
906 free_workspace(type, workspace);
911 * a less complex decompression routine. Our compressed data fits in a
912 * single page, and we want to read a single page out of it.
913 * start_byte tells us the offset into the compressed data we're interested in
915 int btrfs_decompress(int type, unsigned char *data_in, struct page *dest_page,
916 unsigned long start_byte, size_t srclen, size_t destlen)
918 struct list_head *workspace;
921 workspace = find_workspace(type);
922 if (IS_ERR(workspace))
925 ret = btrfs_compress_op[type-1]->decompress(workspace, data_in,
926 dest_page, start_byte,
929 free_workspace(type, workspace);
933 void btrfs_exit_compress(void)
939 * Copy uncompressed data from working buffer to pages.
941 * buf_start is the byte offset we're of the start of our workspace buffer.
943 * total_out is the last byte of the buffer
945 int btrfs_decompress_buf2page(char *buf, unsigned long buf_start,
946 unsigned long total_out, u64 disk_start,
947 struct bio_vec *bvec, int vcnt,
948 unsigned long *page_index,
949 unsigned long *pg_offset)
951 unsigned long buf_offset;
952 unsigned long current_buf_start;
953 unsigned long start_byte;
954 unsigned long working_bytes = total_out - buf_start;
957 struct page *page_out = bvec[*page_index].bv_page;
960 * start byte is the first byte of the page we're currently
961 * copying into relative to the start of the compressed data.
963 start_byte = page_offset(page_out) - disk_start;
965 /* we haven't yet hit data corresponding to this page */
966 if (total_out <= start_byte)
970 * the start of the data we care about is offset into
971 * the middle of our working buffer
973 if (total_out > start_byte && buf_start < start_byte) {
974 buf_offset = start_byte - buf_start;
975 working_bytes -= buf_offset;
979 current_buf_start = buf_start;
981 /* copy bytes from the working buffer into the pages */
982 while (working_bytes > 0) {
983 bytes = min(PAGE_CACHE_SIZE - *pg_offset,
984 PAGE_CACHE_SIZE - buf_offset);
985 bytes = min(bytes, working_bytes);
986 kaddr = kmap_atomic(page_out, KM_USER0);
987 memcpy(kaddr + *pg_offset, buf + buf_offset, bytes);
988 kunmap_atomic(kaddr, KM_USER0);
989 flush_dcache_page(page_out);
993 working_bytes -= bytes;
994 current_buf_start += bytes;
996 /* check if we need to pick another page */
997 if (*pg_offset == PAGE_CACHE_SIZE) {
999 if (*page_index >= vcnt)
1002 page_out = bvec[*page_index].bv_page;
1004 start_byte = page_offset(page_out) - disk_start;
1007 * make sure our new page is covered by this
1010 if (total_out <= start_byte)
1014 * the next page in the biovec might not be adjacent
1015 * to the last page, but it might still be found
1016 * inside this working buffer. bump our offset pointer
1018 if (total_out > start_byte &&
1019 current_buf_start < start_byte) {
1020 buf_offset = start_byte - buf_start;
1021 working_bytes = total_out - start_byte;
1022 current_buf_start = buf_start + buf_offset;