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-rw-r--r--fs/ubifs/file.c62
1 files changed, 30 insertions, 32 deletions
diff --git a/fs/ubifs/file.c b/fs/ubifs/file.c
index 6d34dc7e33e1..2e6481a7701c 100644
--- a/fs/ubifs/file.c
+++ b/fs/ubifs/file.c
@@ -21,34 +21,32 @@
21 */ 21 */
22 22
23/* 23/*
24 * This file implements VFS file and inode operations of regular files, device 24 * This file implements VFS file and inode operations for regular files, device
25 * nodes and symlinks as well as address space operations. 25 * nodes and symlinks as well as address space operations.
26 * 26 *
27 * UBIFS uses 2 page flags: PG_private and PG_checked. PG_private is set if the 27 * UBIFS uses 2 page flags: @PG_private and @PG_checked. @PG_private is set if
28 * page is dirty and is used for budgeting purposes - dirty pages should not be 28 * the page is dirty and is used for optimization purposes - dirty pages are
29 * budgeted. The PG_checked flag is set if full budgeting is required for the 29 * not budgeted so the flag shows that 'ubifs_write_end()' should not release
30 * page e.g., when it corresponds to a file hole or it is just beyond the file 30 * the budget for this page. The @PG_checked flag is set if full budgeting is
31 * size. The budgeting is done in 'ubifs_write_begin()', because it is OK to 31 * required for the page e.g., when it corresponds to a file hole or it is
32 * fail in this function, and the budget is released in 'ubifs_write_end()'. So 32 * beyond the file size. The budgeting is done in 'ubifs_write_begin()', because
33 * the PG_private and PG_checked flags carry the information about how the page 33 * it is OK to fail in this function, and the budget is released in
34 * was budgeted, to make it possible to release the budget properly. 34 * 'ubifs_write_end()'. So the @PG_private and @PG_checked flags carry
35 * information about how the page was budgeted, to make it possible to release
36 * the budget properly.
35 * 37 *
36 * A thing to keep in mind: inode's 'i_mutex' is locked in most VFS operations 38 * A thing to keep in mind: inode @i_mutex is locked in most VFS operations we
37 * we implement. However, this is not true for '->writepage()', which might be 39 * implement. However, this is not true for 'ubifs_writepage()', which may be
38 * called with 'i_mutex' unlocked. For example, when pdflush is performing 40 * called with @i_mutex unlocked. For example, when pdflush is doing background
39 * write-back, it calls 'writepage()' with unlocked 'i_mutex', although the 41 * write-back, it calls 'ubifs_writepage()' with unlocked @i_mutex. At "normal"
40 * inode has 'I_LOCK' flag in this case. At "normal" work-paths 'i_mutex' is 42 * work-paths the @i_mutex is locked in 'ubifs_writepage()', e.g. in the
41 * locked in '->writepage', e.g. in "sys_write -> alloc_pages -> direct reclaim 43 * "sys_write -> alloc_pages -> direct reclaim path". So, in 'ubifs_writepage()'
42 * path'. So, in '->writepage()' we are only guaranteed that the page is 44 * we are only guaranteed that the page is locked.
43 * locked.
44 * 45 *
45 * Similarly, 'i_mutex' does not have to be locked in readpage(), e.g., 46 * Similarly, @i_mutex is not always locked in 'ubifs_readpage()', e.g., the
46 * readahead path does not have it locked ("sys_read -> generic_file_aio_read 47 * read-ahead path does not lock it ("sys_read -> generic_file_aio_read ->
47 * -> ondemand_readahead -> readpage"). In case of readahead, 'I_LOCK' flag is 48 * ondemand_readahead -> readpage"). In case of readahead, @I_LOCK flag is not
48 * not set as well. However, UBIFS disables readahead. 49 * set as well. However, UBIFS disables readahead.
49 *
50 * This, for example means that there might be 2 concurrent '->writepage()'
51 * calls for the same inode, but different inode dirty pages.
52 */ 50 */
53 51
54#include "ubifs.h" 52#include "ubifs.h"
@@ -449,9 +447,9 @@ static int ubifs_write_begin(struct file *file, struct address_space *mapping,
449 /* 447 /*
450 * We change whole page so no need to load it. But we 448 * We change whole page so no need to load it. But we
451 * have to set the @PG_checked flag to make the further 449 * have to set the @PG_checked flag to make the further
452 * code the page is new. This might be not true, but it 450 * code know that the page is new. This might be not
453 * is better to budget more that to read the page from 451 * true, but it is better to budget more than to read
454 * the media. 452 * the page from the media.
455 */ 453 */
456 SetPageChecked(page); 454 SetPageChecked(page);
457 skipped_read = 1; 455 skipped_read = 1;
@@ -497,8 +495,8 @@ static int ubifs_write_begin(struct file *file, struct address_space *mapping,
497 } 495 }
498 496
499 /* 497 /*
500 * Whee, we aquired budgeting quickly - without involving 498 * Whee, we acquired budgeting quickly - without involving
501 * garbage-collection, committing or forceing write-back. We return 499 * garbage-collection, committing or forcing write-back. We return
502 * with @ui->ui_mutex locked if we are appending pages, and unlocked 500 * with @ui->ui_mutex locked if we are appending pages, and unlocked
503 * otherwise. This is an optimization (slightly hacky though). 501 * otherwise. This is an optimization (slightly hacky though).
504 */ 502 */
@@ -562,7 +560,7 @@ static int ubifs_write_end(struct file *file, struct address_space *mapping,
562 560
563 /* 561 /*
564 * Return 0 to force VFS to repeat the whole operation, or the 562 * Return 0 to force VFS to repeat the whole operation, or the
565 * error code if 'do_readpage()' failes. 563 * error code if 'do_readpage()' fails.
566 */ 564 */
567 copied = do_readpage(page); 565 copied = do_readpage(page);
568 goto out; 566 goto out;
@@ -1175,11 +1173,11 @@ static int do_truncation(struct ubifs_info *c, struct inode *inode,
1175 ui->ui_size = inode->i_size; 1173 ui->ui_size = inode->i_size;
1176 /* Truncation changes inode [mc]time */ 1174 /* Truncation changes inode [mc]time */
1177 inode->i_mtime = inode->i_ctime = ubifs_current_time(inode); 1175 inode->i_mtime = inode->i_ctime = ubifs_current_time(inode);
1178 /* The other attributes may be changed at the same time as well */ 1176 /* Other attributes may be changed at the same time as well */
1179 do_attr_changes(inode, attr); 1177 do_attr_changes(inode, attr);
1180
1181 err = ubifs_jnl_truncate(c, inode, old_size, new_size); 1178 err = ubifs_jnl_truncate(c, inode, old_size, new_size);
1182 mutex_unlock(&ui->ui_mutex); 1179 mutex_unlock(&ui->ui_mutex);
1180
1183out_budg: 1181out_budg:
1184 if (budgeted) 1182 if (budgeted)
1185 ubifs_release_budget(c, &req); 1183 ubifs_release_budget(c, &req);