linux-kernel - [PATCH v2 2/2] bcachefs: replace memcpy with memcpy_and_pad for jset_entry

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Message-ID: <20250327144956.1974622-3-nicolescu.roxana@protonmail.com>
Date: Thu, 27 Mar 2025 14:50:09 +0000
From: Roxana Nicolescu <nicolescu.roxana@...tonmail.com>
To: kent.overstreet@...ux.dev, linux-bcachefs@...r.kernel.org, linux-kernel@...r.kernel.org
Cc: mmpgouride@...il.com, skhan@...uxfoundation.org, linux-kernel-mentees@...ts.linux.dev
Subject: [PATCH v2 2/2] bcachefs: replace memcpy with memcpy_and_pad for jset_entry_log->d buff

This was achieved before by zero-ing out the source buffer and then
copying the bytes into the destination buffer. This can also be done with
memcpy_and_pad which will zero out only the destination buffer if its
size is bigger than the size of the source buffer. This is already used in
the same way in journal_transaction_name().

Moreover, zero-ing the source buffer was done twice, first in
__bch2_fs_log_msg() and then in bch2_trans_log_msg(). And this method
may also require allocating some extra memory for the source buffer.

In conclusion, using memcpy_and_pad is better even tough the result is
the same because it brings uniformity with what's already used in
journal_transaction_name, it avoids code duplication and reallocating
extra memory.

Signed-off-by: Roxana Nicolescu <nicolescu.roxana@...tonmail.com>
---
 fs/bcachefs/btree_update.c | 6 ++----
 1 file changed, 2 insertions(+), 4 deletions(-)

diff --git a/fs/bcachefs/btree_update.c b/fs/bcachefs/btree_update.c
index 13d794f201a5..97495b79ca93 100644
--- a/fs/bcachefs/btree_update.c
+++ b/fs/bcachefs/btree_update.c
@@ -826,7 +826,6 @@ int bch2_btree_bit_mod_buffered(struct btree_trans *trans, enum btree_id btree,
 int bch2_trans_log_msg(struct btree_trans *trans, struct printbuf *buf)
 {
 	unsigned u64s = DIV_ROUND_UP(buf->pos, sizeof(u64));
-	prt_chars(buf, '\0', u64s * sizeof(u64) - buf->pos);
 
 	int ret = buf->allocation_failure ? -BCH_ERR_ENOMEM_trans_log_msg : 0;
 	if (ret)
@@ -839,7 +838,7 @@ int bch2_trans_log_msg(struct btree_trans *trans, struct printbuf *buf)
 
 	struct jset_entry_log *l = container_of(e, struct jset_entry_log, entry);
 	journal_entry_init(e, BCH_JSET_ENTRY_log, 0, 1, u64s);
-	memcpy(l->d, buf->buf, buf->pos);
+	memcpy_and_pad(l->d, u64s * sizeof(u64), buf->buf, buf->pos, 0);
 	return 0;
 }
 
@@ -852,7 +851,6 @@ __bch2_fs_log_msg(struct bch_fs *c, unsigned commit_flags, const char *fmt,
 	prt_vprintf(&buf, fmt, args);
 
 	unsigned u64s = DIV_ROUND_UP(buf.pos, sizeof(u64));
-	prt_chars(&buf, '\0', u64s * sizeof(u64) - buf.pos);
 
 	int ret = buf.allocation_failure ? -BCH_ERR_ENOMEM_trans_log_msg : 0;
 	if (ret)
@@ -865,7 +863,7 @@ __bch2_fs_log_msg(struct bch_fs *c, unsigned commit_flags, const char *fmt,
 
 		struct jset_entry_log *l = (void *) &darray_top(c->journal.early_journal_entries);
 		journal_entry_init(&l->entry, BCH_JSET_ENTRY_log, 0, 1, u64s);
-		memcpy(l->d, buf.buf, buf.pos);
+		memcpy_and_pad(l->d, u64s * sizeof(u64), buf.buf, buf.pos, 0);
 		c->journal.early_journal_entries.nr += jset_u64s(u64s);
 	} else {
 		ret = bch2_trans_commit_do(c, NULL, NULL, commit_flags,
-- 
2.34.1