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UBIFS: amend commentaries

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This patch amends and nicifies commentaries in file.c, as well as
fixes some spelling problems.

Signed-off-by: Artem Bityutskiy <Artem.Bityutskiy@nokia.com>
This commit is contained in:
Artem Bityutskiy 2009-09-01 17:06:43 +03:00
parent 0dcd18e407
commit 873a64c762
1 changed files with 30 additions and 32 deletions
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62
fs/ubifs/file.c
View file

@ -21,34 +21,32 @@
*/
/*
* This file implements VFS file and inode operations of regular files, device
* This file implements VFS file and inode operations for regular files, device
* nodes and symlinks as well as address space operations.
*
* UBIFS uses 2 page flags: PG_private and PG_checked. PG_private is set if the
* page is dirty and is used for budgeting purposes - dirty pages should not be
* budgeted. The PG_checked flag is set if full budgeting is required for the
* page e.g., when it corresponds to a file hole or it is just beyond the file
* size. The budgeting is done in 'ubifs_write_begin()', because it is OK to
* fail in this function, and the budget is released in 'ubifs_write_end()'. So
* the PG_private and PG_checked flags carry the information about how the page
* was budgeted, to make it possible to release the budget properly.
* UBIFS uses 2 page flags: @PG_private and @PG_checked. @PG_private is set if
* the page is dirty and is used for optimization purposes - dirty pages are
* not budgeted so the flag shows that 'ubifs_write_end()' should not release
* the budget for this page. The @PG_checked flag is set if full budgeting is
* required for the page e.g., when it corresponds to a file hole or it is
* beyond the file size. The budgeting is done in 'ubifs_write_begin()', because
* it is OK to fail in this function, and the budget is released in
* 'ubifs_write_end()'. So the @PG_private and @PG_checked flags carry
* information about how the page was budgeted, to make it possible to release
* the budget properly.
*
* A thing to keep in mind: inode's 'i_mutex' is locked in most VFS operations
* we implement. However, this is not true for '->writepage()', which might be
* called with 'i_mutex' unlocked. For example, when pdflush is performing
* write-back, it calls 'writepage()' with unlocked 'i_mutex', although the
* inode has 'I_LOCK' flag in this case. At "normal" work-paths 'i_mutex' is
* locked in '->writepage', e.g. in "sys_write -> alloc_pages -> direct reclaim
* path'. So, in '->writepage()' we are only guaranteed that the page is
* locked.
* A thing to keep in mind: inode @i_mutex is locked in most VFS operations we
* implement. However, this is not true for 'ubifs_writepage()', which may be
* called with @i_mutex unlocked. For example, when pdflush is doing background
* write-back, it calls 'ubifs_writepage()' with unlocked @i_mutex. At "normal"
* work-paths the @i_mutex is locked in 'ubifs_writepage()', e.g. in the
* "sys_write -> alloc_pages -> direct reclaim path". So, in 'ubifs_writepage()'
* we are only guaranteed that the page is locked.
*
* Similarly, 'i_mutex' does not have to be locked in readpage(), e.g.,
* readahead path does not have it locked ("sys_read -> generic_file_aio_read
* -> ondemand_readahead -> readpage"). In case of readahead, 'I_LOCK' flag is
* not set as well. However, UBIFS disables readahead.
*
* This, for example means that there might be 2 concurrent '->writepage()'
* calls for the same inode, but different inode dirty pages.
* Similarly, @i_mutex is not always locked in 'ubifs_readpage()', e.g., the
* read-ahead path does not lock it ("sys_read -> generic_file_aio_read ->
* ondemand_readahead -> readpage"). In case of readahead, @I_LOCK flag is not
* set as well. However, UBIFS disables readahead.
*/
#include "ubifs.h"
@ -449,9 +447,9 @@ static int ubifs_write_begin(struct file *file, struct address_space *mapping,
/*
* We change whole page so no need to load it. But we
* have to set the @PG_checked flag to make the further
* code the page is new. This might be not true, but it
* is better to budget more that to read the page from
* the media.
* code know that the page is new. This might be not
* true, but it is better to budget more than to read
* the page from the media.
*/
SetPageChecked(page);
skipped_read = 1;
@ -497,8 +495,8 @@ static int ubifs_write_begin(struct file *file, struct address_space *mapping,
}
/*
* Whee, we aquired budgeting quickly - without involving
* garbage-collection, committing or forceing write-back. We return
* Whee, we acquired budgeting quickly - without involving
* garbage-collection, committing or forcing write-back. We return
* with @ui->ui_mutex locked if we are appending pages, and unlocked
* otherwise. This is an optimization (slightly hacky though).
*/
@ -562,7 +560,7 @@ static int ubifs_write_end(struct file *file, struct address_space *mapping,
/*
* Return 0 to force VFS to repeat the whole operation, or the
* error code if 'do_readpage()' failes.
* error code if 'do_readpage()' fails.
*/
copied = do_readpage(page);
goto out;
@ -1175,11 +1173,11 @@ static int do_truncation(struct ubifs_info *c, struct inode *inode,
ui->ui_size = inode->i_size;
/* Truncation changes inode [mc]time */
inode->i_mtime = inode->i_ctime = ubifs_current_time(inode);
/* The other attributes may be changed at the same time as well */
/* Other attributes may be changed at the same time as well */
do_attr_changes(inode, attr);
err = ubifs_jnl_truncate(c, inode, old_size, new_size);
mutex_unlock(&ui->ui_mutex);
out_budg:
if (budgeted)
ubifs_release_budget(c, &req);