linux-ext4 - [PATCH 10/11] ext4: Shortcut setting of xattr to the same value

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Date:	Mon, 22 Feb 2016 08:48:20 +0100
From:	Jan Kara <jack@...e.cz>
To:	Ted Tso <tytso@....edu>
Cc:	Andreas Gruenbacher <agruenba@...hat.com>,
	linux-ext4@...r.kernel.org, Jan Kara <jack@...e.cz>
Subject: [PATCH 10/11] ext4: Shortcut setting of xattr to the same value

When someone tried to set xattr to the same value (i.e., not changing
anything) we did all the work of removing original xattr, possibly
breaking references to shared xattr block, inserting new xattr, and
merging xattr blocks again. Since this is not so rare operation and it
is relatively cheap for us to detect this case, check for this and
shortcut xattr setting in that case.

Signed-off-by: Jan Kara <jack@...e.cz>
---
 fs/ext4/xattr.c | 18 ++++++++++++++++++
 1 file changed, 18 insertions(+)

diff --git a/fs/ext4/xattr.c b/fs/ext4/xattr.c
index c6af8a7a436a..b661ae8332e3 100644
--- a/fs/ext4/xattr.c
+++ b/fs/ext4/xattr.c
@@ -1096,6 +1096,17 @@ static int ext4_xattr_ibody_set(handle_t *handle, struct inode *inode,
 	return 0;
 }
 
+static int ext4_xattr_value_same(struct ext4_xattr_search *s,
+				 struct ext4_xattr_info *i)
+{
+	void *value;
+
+	if (le32_to_cpu(s->here->e_value_size) != i->value_len)
+		return 0;
+	value = ((void *)s->base) + le16_to_cpu(s->here->e_value_offs);
+	return !memcmp(value, i->value, i->value_len);
+}
+
 /*
  * ext4_xattr_set_handle()
  *
@@ -1172,6 +1183,13 @@ ext4_xattr_set_handle(handle_t *handle, struct inode *inode, int name_index,
 		else if (!bs.s.not_found)
 			error = ext4_xattr_block_set(handle, inode, &i, &bs);
 	} else {
+		error = 0;
+		/* Xattr value did not change? Save us some work and bail out */
+		if (!is.s.not_found && ext4_xattr_value_same(&is.s, &i))
+			goto cleanup;
+		if (!bs.s.not_found && ext4_xattr_value_same(&bs.s, &i))
+			goto cleanup;
+
 		error = ext4_xattr_ibody_set(handle, inode, &i, &is);
 		if (!error && !bs.s.not_found) {
 			i.value = NULL;
-- 
2.6.2

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