[PATCH v12 4/7] fsdax: Introduce dax_lock_mapping_entry()

Shiyang Ruan
2022-04-10T16:09:26Z

The current dax_lock_page() locks dax entry by obtaining mapping and
index in page. To support 1-to-N RMAP in NVDIMM, we need a new function
to lock a specific dax entry corresponding to this file's mapping,index.
And output the page corresponding to the specific dax entry for caller
use.

Signed-off-by: Shiyang Ruan <ruansy.fnst@fujitsu.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
---
fs/dax.c | 63 +++++++++++++++++++++++++++++++++++++++++++++
include/linux/dax.h | 15 +++++++++++
2 files changed, 78 insertions(+)

diff --git a/fs/dax.c b/fs/dax.c
index 1ac12e877f4f..57efd3f73655 100644
--- a/fs/dax.c
+++ b/fs/dax.c
@@ -455,6 +455,69 @@ void dax_unlock_page(struct page *page, dax_entry_t cookie)
dax_unlock_entry(&xas, (void *)cookie);
}

+/*
+ * dax_lock_mapping_entry - Lock the DAX entry corresponding to a mapping
+ * @mapping: the file's mapping whose entry we want to lock
+ * @index: the offset within this file
+ * @page: output the dax page corresponding to this dax entry
+ *
+ * Return: A cookie to pass to dax_unlock_mapping_entry() or 0 if the entry
+ * could not be locked.
+ */
+dax_entry_t dax_lock_mapping_entry(struct address_space *mapping, pgoff_t index,
+ struct page **page)
+{
+ XA_STATE(xas, NULL, 0);
+ void *entry;
+
+ rcu_read_lock();
+ for (;;) {
+ entry = NULL;
+ if (!dax_mapping(mapping))
+ break;
+
+ xas.xa = &mapping->i_pages;
+ xas_lock_irq(&xas);
+ xas_set(&xas, index);
+ entry = xas_load(&xas);
+ if (dax_is_locked(entry)) {
+ rcu_read_unlock();
+ wait_entry_unlocked(&xas, entry);
+ rcu_read_lock();
+ continue;
+ }
+ if (!entry ||
+ dax_is_zero_entry(entry) || dax_is_empty_entry(entry)) {
+ /*
+ * Because we are looking for entry from file's mapping
+ * and index, so the entry may not be inserted for now,
+ * or even a zero/empty entry. We don't think this is
+ * an error case. So, return a special value and do
+ * not output @page.
+ */
+ entry = (void *)~0UL;
+ } else {
+ *page = pfn_to_page(dax_to_pfn(entry));
+ dax_lock_entry(&xas, entry);
+ }
+ xas_unlock_irq(&xas);
+ break;
+ }
+ rcu_read_unlock();
+ return (dax_entry_t)entry;
+}
+
+void dax_unlock_mapping_entry(struct address_space *mapping, pgoff_t index,
+ dax_entry_t cookie)
+{
+ XA_STATE(xas, &mapping->i_pages, index);
+
+ if (cookie == ~0UL)
+ return;
+
+ dax_unlock_entry(&xas, (void *)cookie);
+}
+
/*
* Find page cache entry at given index. If it is a DAX entry, return it
* with the entry locked. If the page cache doesn't contain an entry at
diff --git a/include/linux/dax.h b/include/linux/dax.h
index 9c426a207ba8..c152f315d1c9 100644
--- a/include/linux/dax.h
+++ b/include/linux/dax.h
@@ -143,6 +143,10 @@ struct page *dax_layout_busy_page(struct address_space *mapping);
struct page *dax_layout_busy_page_range(struct address_space *mapping, loff_t start, loff_t end);
dax_entry_t dax_lock_page(struct page *page);
void dax_unlock_page(struct page *page, dax_entry_t cookie);
+dax_entry_t dax_lock_mapping_entry(struct address_space *mapping,
+ unsigned long index, struct page **page);
+void dax_unlock_mapping_entry(struct address_space *mapping,
+ unsigned long index, dax_entry_t cookie);
#else
static inline struct page *dax_layout_busy_page(struct address_space *mapping)
{
@@ -170,6 +174,17 @@ static inline dax_entry_t dax_lock_page(struct page *page)
static inline void dax_unlock_page(struct page *page, dax_entry_t cookie)
{
}
+
+static inline dax_entry_t dax_lock_mapping_entry(struct address_space *mapping,
+ unsigned long index, struct page **page)
+{
+ return 0;
+}
+
+static inline void dax_unlock_mapping_entry(struct address_space *mapping,
+ unsigned long index, dax_entry_t cookie)
+{
+}
#endif

int dax_zero_range(struct inode *inode, loff_t pos, loff_t len, bool *did_zero,
--
2.35.1