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Message-ID: <87r6vkzinv.fsf@duaron.myhome.or.jp>
Date: Fri, 01 Dec 2006 07:14:28 +0900
From: OGAWA Hirofumi <hirofumi@...l.parknet.co.jp>
To: Nick Piggin <npiggin@...e.de>
Cc: Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
Andrew Morton <akpm@...l.org>, linux-fsdevel@...r.kernel.org
Subject: Re: [patch 3/3] fs: fix cont vs deadlock patches
Nick Piggin <npiggin@...e.de> writes:
> Rework the cont filesystem helpers so that generic_cont_expand does the
> actual work of expanding the file. cont_prepare_write then calls this
> routine if expanding is needed, and retries. Also solves the problem
> where cont_prepare_write would previously hold the target page locked
> while doing not-very-nice things like locking other pages.
>
> Means that zero-length prepare/commit_write pairs are no longer needed
> as an overloaded directive to extend the file, thus cont should operate
> better within the new deadlock-free buffered write code.
>
> Converts fat over to the new cont scheme.
>
> Signed-off-by: Nick Piggin <npiggin@...e.de>
>
>
> Index: linux-2.6/fs/buffer.c
> ===================================================================
> --- linux-2.6.orig/fs/buffer.c
> +++ linux-2.6/fs/buffer.c
> @@ -2004,19 +2004,20 @@ int block_read_full_page(struct page *pa
> return 0;
> }
>
> -/* utility function for filesystems that need to do work on expanding
> - * truncates. Uses prepare/commit_write to allow the filesystem to
> - * deal with the hole.
> +/*
> + * Utility function for filesystems that need to do work on expanding
> + * truncates. For moronic filesystems that do not allow holes in file.
> */
> -static int __generic_cont_expand(struct inode *inode, loff_t size,
> - pgoff_t index, unsigned int offset)
> +int generic_cont_expand(struct inode *inode, loff_t size, loff_t *bytes,
> + get_block_t *get_block)
> {
> struct address_space *mapping = inode->i_mapping;
> + unsigned long blocksize = 1 << inode->i_blkbits;
> struct page *page;
> unsigned long limit;
> - int err;
> + int status;
>
> - err = -EFBIG;
> + status = -EFBIG;
> limit = current->signal->rlim[RLIMIT_FSIZE].rlim_cur;
> if (limit != RLIM_INFINITY && size > (loff_t)limit) {
> send_sig(SIGXFSZ, current, 0);
> @@ -2025,146 +2026,83 @@ static int __generic_cont_expand(struct
> if (size > inode->i_sb->s_maxbytes)
> goto out;
>
> - err = -ENOMEM;
> - page = grab_cache_page(mapping, index);
> - if (!page)
> - goto out;
> - err = mapping->a_ops->prepare_write(NULL, page, offset, offset);
> - if (err) {
> - /*
> - * ->prepare_write() may have instantiated a few blocks
> - * outside i_size. Trim these off again.
> - */
> - unlock_page(page);
> - page_cache_release(page);
> - vmtruncate(inode, inode->i_size);
> - goto out;
> - }
> + status = 0;
>
> - err = mapping->a_ops->commit_write(NULL, page, offset, offset);
> + while (*bytes < size) {
> + unsigned int zerofrom;
> + unsigned int zeroto;
> + void *kaddr;
> + pgoff_t pgpos;
> +
> + pgpos = *bytes >> PAGE_CACHE_SHIFT;
> + page = grab_cache_page(mapping, pgpos);
> + if (!page) {
> + status = -ENOMEM;
> + break;
> + }
> + /* we might sleep */
> + if (*bytes >> PAGE_CACHE_SHIFT != pgpos)
> + goto unlock;
>
> - unlock_page(page);
> - page_cache_release(page);
> - if (err > 0)
> - err = 0;
> -out:
> - return err;
> -}
> + zerofrom = *bytes & ~PAGE_CACHE_MASK;
> + if (zerofrom & (blocksize-1))
> + *bytes = (*bytes + blocksize-1) & (blocksize-1);
>
> -int generic_cont_expand(struct inode *inode, loff_t size)
> -{
> - pgoff_t index;
> - unsigned int offset;
> + zeroto = PAGE_CACHE_SIZE;
>
> - offset = (size & (PAGE_CACHE_SIZE - 1)); /* Within page */
> + status = __block_prepare_write(inode, page, zerofrom,
> + zeroto, get_block);
> + if (status)
> + goto unlock;
> + kaddr = kmap_atomic(page, KM_USER0);
> + memset(kaddr+zerofrom, 0, PAGE_CACHE_SIZE-zerofrom);
> + flush_dcache_page(page);
> + kunmap_atomic(kaddr, KM_USER0);
> + status = __block_commit_write(inode, page, zerofrom, zeroto);
>
> - /* ugh. in prepare/commit_write, if from==to==start of block, we
> - ** skip the prepare. make sure we never send an offset for the start
> - ** of a block
> - */
> - if ((offset & (inode->i_sb->s_blocksize - 1)) == 0) {
> - /* caller must handle this extra byte. */
> - offset++;
> +unlock:
> + unlock_page(page);
> + page_cache_release(page);
> + if (status) {
> + BUG_ON(status == AOP_TRUNCATED_PAGE);
> + break;
> + }
> }
> - index = size >> PAGE_CACHE_SHIFT;
>
> - return __generic_cont_expand(inode, size, index, offset);
> -}
> -
> -int generic_cont_expand_simple(struct inode *inode, loff_t size)
> -{
> - loff_t pos = size - 1;
> - pgoff_t index = pos >> PAGE_CACHE_SHIFT;
> - unsigned int offset = (pos & (PAGE_CACHE_SIZE - 1)) + 1;
> + /*
> + * No need to use i_size_read() here, the i_size
> + * cannot change under us because we hold i_mutex.
> + */
> + if (size > inode->i_size) {
> + i_size_write(inode, size);
> + mark_inode_dirty(inode);
> + }
>
> - /* prepare/commit_write can handle even if from==to==start of block. */
> - return __generic_cont_expand(inode, size, index, offset);
> +out:
> + return status;
> }
quick look. Doesn't this break reiserfs? IIRC, the reiserfs is using
it for another reason. I was also working for this, but I lost the
thread of this, sorry.
I found some another users (affs, hfs, hfsplus). Those seem have same
problem, but probably those also can use this...
What do you think?
--
OGAWA Hirofumi <hirofumi@...l.parknet.co.jp>
Signed-off-by: OGAWA Hirofumi <hirofumi@...l.parknet.co.jp>
---
fs/buffer.c | 59 +++++++++++++++++---------------------------
fs/fat/file.c | 2 -
include/linux/buffer_head.h | 1
3 files changed, 24 insertions(+), 38 deletions(-)
diff -puN fs/buffer.c~generic_cont_expand-avoid-zero-size fs/buffer.c
--- linux-2.6/fs/buffer.c~generic_cont_expand-avoid-zero-size 2006-11-13 01:42:01.000000000 +0900
+++ linux-2.6-hirofumi/fs/buffer.c 2006-11-13 02:16:20.000000000 +0900
@@ -2004,18 +2004,24 @@ int block_read_full_page(struct page *pa
return 0;
}
-/* utility function for filesystems that need to do work on expanding
+/*
+ * utility function for filesystems that need to do work on expanding
* truncates. Uses prepare/commit_write to allow the filesystem to
* deal with the hole.
*/
-static int __generic_cont_expand(struct inode *inode, loff_t size,
- pgoff_t index, unsigned int offset)
+int generic_cont_expand(struct inode *inode, loff_t size)
{
struct address_space *mapping = inode->i_mapping;
+ loff_t pos = inode->i_size;
struct page *page;
unsigned long limit;
+ pgoff_t index;
+ unsigned int from, to;
+ void *kaddr;
int err;
+ WARN_ON(pos >= size);
+
err = -EFBIG;
limit = current->signal->rlim[RLIMIT_FSIZE].rlim_cur;
if (limit != RLIM_INFINITY && size > (loff_t)limit) {
@@ -2025,11 +2031,18 @@ static int __generic_cont_expand(struct
if (size > inode->i_sb->s_maxbytes)
goto out;
+ index = (size - 1) >> PAGE_CACHE_SHIFT;
+ to = size - ((loff_t)index << PAGE_CACHE_SHIFT);
+ if (index != (pos >> PAGE_CACHE_SHIFT))
+ from = 0;
+ else
+ from = pos & (PAGE_CACHE_SIZE - 1);
+
err = -ENOMEM;
page = grab_cache_page(mapping, index);
if (!page)
goto out;
- err = mapping->a_ops->prepare_write(NULL, page, offset, offset);
+ err = mapping->a_ops->prepare_write(NULL, page, from, to);
if (err) {
/*
* ->prepare_write() may have instantiated a few blocks
@@ -2041,7 +2054,12 @@ static int __generic_cont_expand(struct
goto out;
}
- err = mapping->a_ops->commit_write(NULL, page, offset, offset);
+ kaddr = kmap_atomic(page, KM_USER0);
+ memset(kaddr + from, 0, to - from);
+ flush_dcache_page(page);
+ kunmap_atomic(kaddr, KM_USER0);
+
+ err = mapping->a_ops->commit_write(NULL, page, from, to);
unlock_page(page);
page_cache_release(page);
@@ -2051,36 +2069,6 @@ out:
return err;
}
-int generic_cont_expand(struct inode *inode, loff_t size)
-{
- pgoff_t index;
- unsigned int offset;
-
- offset = (size & (PAGE_CACHE_SIZE - 1)); /* Within page */
-
- /* ugh. in prepare/commit_write, if from==to==start of block, we
- ** skip the prepare. make sure we never send an offset for the start
- ** of a block
- */
- if ((offset & (inode->i_sb->s_blocksize - 1)) == 0) {
- /* caller must handle this extra byte. */
- offset++;
- }
- index = size >> PAGE_CACHE_SHIFT;
-
- return __generic_cont_expand(inode, size, index, offset);
-}
-
-int generic_cont_expand_simple(struct inode *inode, loff_t size)
-{
- loff_t pos = size - 1;
- pgoff_t index = pos >> PAGE_CACHE_SHIFT;
- unsigned int offset = (pos & (PAGE_CACHE_SIZE - 1)) + 1;
-
- /* prepare/commit_write can handle even if from==to==start of block. */
- return __generic_cont_expand(inode, size, index, offset);
-}
-
/*
* For moronic filesystems that do not allow holes in file.
* We may have to extend the file.
@@ -3032,7 +3020,6 @@ EXPORT_SYMBOL(fsync_bdev);
EXPORT_SYMBOL(generic_block_bmap);
EXPORT_SYMBOL(generic_commit_write);
EXPORT_SYMBOL(generic_cont_expand);
-EXPORT_SYMBOL(generic_cont_expand_simple);
EXPORT_SYMBOL(init_buffer);
EXPORT_SYMBOL(invalidate_bdev);
EXPORT_SYMBOL(ll_rw_block);
diff -puN include/linux/buffer_head.h~generic_cont_expand-avoid-zero-size include/linux/buffer_head.h
--- linux-2.6/include/linux/buffer_head.h~generic_cont_expand-avoid-zero-size 2006-11-13 01:42:01.000000000 +0900
+++ linux-2.6-hirofumi/include/linux/buffer_head.h 2006-11-13 01:42:01.000000000 +0900
@@ -202,7 +202,6 @@ int block_prepare_write(struct page*, un
int cont_prepare_write(struct page*, unsigned, unsigned, get_block_t*,
loff_t *);
int generic_cont_expand(struct inode *inode, loff_t size);
-int generic_cont_expand_simple(struct inode *inode, loff_t size);
int block_commit_write(struct page *page, unsigned from, unsigned to);
void block_sync_page(struct page *);
sector_t generic_block_bmap(struct address_space *, sector_t, get_block_t *);
diff -puN fs/fat/file.c~generic_cont_expand-avoid-zero-size fs/fat/file.c
--- linux-2.6/fs/fat/file.c~generic_cont_expand-avoid-zero-size 2006-11-13 01:42:01.000000000 +0900
+++ linux-2.6-hirofumi/fs/fat/file.c 2006-11-13 01:42:01.000000000 +0900
@@ -143,7 +143,7 @@ static int fat_cont_expand(struct inode
loff_t start = inode->i_size, count = size - inode->i_size;
int err;
- err = generic_cont_expand_simple(inode, size);
+ err = generic_cont_expand(inode, size);
if (err)
goto out;
_
-
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