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xfs: Introduce a helper routine to probe data or hole offset from page cache

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Introduce helpers to probe data or hole offset from page cache.

Signed-off-by: Jie Liu <jeff.liu@oracle.com>
Reviewed-by: Mark Tinguely <tinguely@sgi.com>
Reviewed-by: Dave Chinner <dchinner@redhat.com>
Signed-off-by: Ben Myers <bpm@sgi.com>
This commit is contained in:
Jeff Liu
2012-08-21 17:11:57 +08:00
committed by Ben Myers
parent 834ab12228
commit d126d43f63
1 changed files with 219 additions and 0 deletions
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219
fs/xfs/xfs_file.c
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@@ -36,6 +36,7 @@
#include <linux/dcache.h> #include <linux/dcache.h>
#include <linux/falloc.h> #include <linux/falloc.h>
#include <linux/pagevec.h>
static const struct vm_operations_struct xfs_file_vm_ops; static const struct vm_operations_struct xfs_file_vm_ops;
@@ -959,6 +960,224 @@ xfs_vm_page_mkwrite(
return block_page_mkwrite(vma, vmf, xfs_get_blocks); return block_page_mkwrite(vma, vmf, xfs_get_blocks);
} }
/*
* This type is designed to indicate the type of offset we would like
* to search from page cache for either xfs_seek_data() or xfs_seek_hole().
*/
enum {
HOLE_OFF = 0,
DATA_OFF,
};
/*
* Lookup the desired type of offset from the given page.
*
* On success, return true and the offset argument will point to the
* start of the region that was found. Otherwise this function will
* return false and keep the offset argument unchanged.
*/
STATIC bool
xfs_lookup_buffer_offset(
struct page *page,
loff_t *offset,
unsigned int type)
{
loff_t lastoff = page_offset(page);
bool found = false;
struct buffer_head *bh, *head;
bh = head = page_buffers(page);
do {
/*
* Unwritten extents that have data in the page
* cache covering them can be identified by the
* BH_Unwritten state flag. Pages with multiple
* buffers might have a mix of holes, data and
* unwritten extents - any buffer with valid
* data in it should have BH_Uptodate flag set
* on it.
*/
if (buffer_unwritten(bh) ||
buffer_uptodate(bh)) {
if (type == DATA_OFF)
found = true;
} else {
if (type == HOLE_OFF)
found = true;
}
if (found) {
*offset = lastoff;
break;
}
lastoff += bh->b_size;
} while ((bh = bh->b_this_page) != head);
return found;
}
/*
* This routine is called to find out and return a data or hole offset
* from the page cache for unwritten extents according to the desired
* type for xfs_seek_data() or xfs_seek_hole().
*
* The argument offset is used to tell where we start to search from the
* page cache. Map is used to figure out the end points of the range to
* lookup pages.
*
* Return true if the desired type of offset was found, and the argument
* offset is filled with that address. Otherwise, return false and keep
* offset unchanged.
*/
STATIC bool
xfs_find_get_desired_pgoff(
struct inode *inode,
struct xfs_bmbt_irec *map,
unsigned int type,
loff_t *offset)
{
struct xfs_inode *ip = XFS_I(inode);
struct xfs_mount *mp = ip->i_mount;
struct pagevec pvec;
pgoff_t index;
pgoff_t end;
loff_t endoff;
loff_t startoff = *offset;
loff_t lastoff = startoff;
bool found = false;
pagevec_init(&pvec, 0);
index = startoff >> PAGE_CACHE_SHIFT;
endoff = XFS_FSB_TO_B(mp, map->br_startoff + map->br_blockcount);
end = endoff >> PAGE_CACHE_SHIFT;
do {
int want;
unsigned nr_pages;
unsigned int i;
want = min_t(pgoff_t, end - index, PAGEVEC_SIZE);
nr_pages = pagevec_lookup(&pvec, inode->i_mapping, index,
want);
/*
* No page mapped into given range. If we are searching holes
* and if this is the first time we got into the loop, it means
* that the given offset is landed in a hole, return it.
*
* If we have already stepped through some block buffers to find
* holes but they all contains data. In this case, the last
* offset is already updated and pointed to the end of the last
* mapped page, if it does not reach the endpoint to search,
* that means there should be a hole between them.
*/
if (nr_pages == 0) {
/* Data search found nothing */
if (type == DATA_OFF)
break;
ASSERT(type == HOLE_OFF);
if (lastoff == startoff || lastoff < endoff) {
found = true;
*offset = lastoff;
}
break;
}
/*
* At lease we found one page. If this is the first time we
* step into the loop, and if the first page index offset is
* greater than the given search offset, a hole was found.
*/
if (type == HOLE_OFF && lastoff == startoff &&
lastoff < page_offset(pvec.pages[0])) {
found = true;
break;
}
for (i = 0; i < nr_pages; i++) {
struct page *page = pvec.pages[i];
loff_t b_offset;
/*
* At this point, the page may be truncated or
* invalidated (changing page->mapping to NULL),
* or even swizzled back from swapper_space to tmpfs
* file mapping. However, page->index will not change
* because we have a reference on the page.
*
* Searching done if the page index is out of range.
* If the current offset is not reaches the end of
* the specified search range, there should be a hole
* between them.
*/
if (page->index > end) {
if (type == HOLE_OFF && lastoff < endoff) {
*offset = lastoff;
found = true;
}
goto out;
}
lock_page(page);
/*
* Page truncated or invalidated(page->mapping == NULL).
* We can freely skip it and proceed to check the next
* page.
*/
if (unlikely(page->mapping != inode->i_mapping)) {
unlock_page(page);
continue;
}
if (!page_has_buffers(page)) {
unlock_page(page);
continue;
}
found = xfs_lookup_buffer_offset(page, &b_offset, type);
if (found) {
/*
* The found offset may be less than the start
* point to search if this is the first time to
* come here.
*/
*offset = max_t(loff_t, startoff, b_offset);
unlock_page(page);
goto out;
}
/*
* We either searching data but nothing was found, or
* searching hole but found a data buffer. In either
* case, probably the next page contains the desired
* things, update the last offset to it so.
*/
lastoff = page_offset(page) + PAGE_SIZE;
unlock_page(page);
}
/*
* The number of returned pages less than our desired, search
* done. In this case, nothing was found for searching data,
* but we found a hole behind the last offset.
*/
if (nr_pages < want) {
if (type == HOLE_OFF) {
*offset = lastoff;
found = true;
}
break;
}
index = pvec.pages[i - 1]->index + 1;
pagevec_release(&pvec);
} while (index <= end);
out:
pagevec_release(&pvec);
return found;
}
STATIC loff_t STATIC loff_t
xfs_seek_data( xfs_seek_data(
struct file *file, struct file *file,