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Subject[PATCH] staging: erofs: harden inode lookup for 32-bit platforms
Date
This patch introduces inode hash function, test and set callbacks,
and iget5_locked to find the right inode for 32-bit platforms.

Reviewed-by: Chao Yu <yuchao0@huawei.com>
Signed-off-by: Gao Xiang <gaoxiang25@huawei.com>
---

The patch has been previewed in the linux-erofs mailing list, submit to
the staging mailing list for linux-4.20.

Thanks,
Gao Xiang

drivers/staging/erofs/inode.c | 37 ++++++++++++++++++++++++++++++++++++-
drivers/staging/erofs/internal.h | 9 +++++++++
2 files changed, 45 insertions(+), 1 deletion(-)

diff --git a/drivers/staging/erofs/inode.c b/drivers/staging/erofs/inode.c
index da8693a7c3d3..04c61a9d7b76 100644
--- a/drivers/staging/erofs/inode.c
+++ b/drivers/staging/erofs/inode.c
@@ -232,10 +232,45 @@ static int fill_inode(struct inode *inode, int isdir)
return err;
}

+/*
+ * erofs nid is 64bits, but i_ino is 'unsigned long', therefore
+ * we should do more for 32-bit platform to find the right inode.
+ */
+#if BITS_PER_LONG == 32
+static int erofs_ilookup_test_actor(struct inode *inode, void *opaque)
+{
+ const erofs_nid_t nid = *(erofs_nid_t *)opaque;
+
+ return EROFS_V(inode)->nid == nid;
+}
+
+static int erofs_iget_set_actor(struct inode *inode, void *opaque)
+{
+ const erofs_nid_t nid = *(erofs_nid_t *)opaque;
+
+ inode->i_ino = erofs_inode_hash(nid);
+ return 0;
+}
+#endif
+
+static inline struct inode *erofs_iget_locked(struct super_block *sb,
+ erofs_nid_t nid)
+{
+ const unsigned long hashval = erofs_inode_hash(nid);
+
+#if BITS_PER_LONG >= 64
+ /* it is safe to use iget_locked for >= 64-bit platform */
+ return iget_locked(sb, hashval);
+#else
+ return iget5_locked(sb, hashval, erofs_ilookup_test_actor,
+ erofs_iget_set_actor, &nid);
+#endif
+}
+
struct inode *erofs_iget(struct super_block *sb,
erofs_nid_t nid, bool isdir)
{
- struct inode *inode = iget_locked(sb, nid);
+ struct inode *inode = erofs_iget_locked(sb, nid);

if (unlikely(inode == NULL))
return ERR_PTR(-ENOMEM);
diff --git a/drivers/staging/erofs/internal.h b/drivers/staging/erofs/internal.h
index 5096b27bcf0d..57575c7f5635 100644
--- a/drivers/staging/erofs/internal.h
+++ b/drivers/staging/erofs/internal.h
@@ -517,6 +517,15 @@ erofs_get_inline_page(struct inode *inode,
}

/* inode.c */
+static inline unsigned long erofs_inode_hash(erofs_nid_t nid)
+{
+#if BITS_PER_LONG == 32
+ return (nid >> 32) ^ (nid & 0xffffffff);
+#else
+ return nid;
+#endif
+}
+
extern struct inode *erofs_iget(struct super_block *sb,
erofs_nid_t nid, bool dir);

--
2.14.4
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