From 29c336afebb9013706334c1b451f31fe5ff37f34 Mon Sep 17 00:00:00 2001 From: Joshua Ashton Date: Sat, 12 Aug 2023 22:26:30 +0100 Subject: [PATCH] bcachefs: Optimize bch2_dirent_name_bytes Avoids doing a full strnlen for getting the length of the name of a dirent entry. Given the fact that the name of dirents is stored at the end of the bkey's value, and we know the length of that in u64s, we can find the last u64 and figure out how many NUL bytes are at the end of the string. On little endian systems this ends up being the leading zeros of the last u64, whereas on big endian systems this ends up being the trailing zeros of the last u64. We can take that value in bits and divide it by 8 to get the number of NUL bytes at the end. There is no endian-fixup or other compatibility here as this is string data interpreted as a u64. Signed-off-by: Joshua Ashton Signed-off-by: Kent Overstreet --- fs/bcachefs/dirent.c | 21 +++++++++++++++++---- 1 file changed, 17 insertions(+), 4 deletions(-) diff --git a/fs/bcachefs/dirent.c b/fs/bcachefs/dirent.c index a87c4e5f089d2..6f9eb88c7dba9 100644 --- a/fs/bcachefs/dirent.c +++ b/fs/bcachefs/dirent.c @@ -15,10 +15,18 @@ static unsigned bch2_dirent_name_bytes(struct bkey_s_c_dirent d) { - unsigned len = bkey_val_bytes(d.k) - - offsetof(struct bch_dirent, d_name); - - return strnlen(d.v->d_name, len); + unsigned bkey_u64s = bkey_val_u64s(d.k); + unsigned bkey_bytes = bkey_u64s * sizeof(u64); + u64 last_u64 = ((u64*)d.v)[bkey_u64s - 1]; +#if CPU_BIG_ENDIAN + unsigned trailing_nuls = last_u64 ? __builtin_ctzll(last_u64) / 8 : 64 / 8; +#else + unsigned trailing_nuls = last_u64 ? __builtin_clzll(last_u64) / 8 : 64 / 8; +#endif + + return bkey_bytes - + offsetof(struct bch_dirent, d_name) - + trailing_nuls; } struct qstr bch2_dirent_get_name(struct bkey_s_c_dirent d) @@ -113,6 +121,11 @@ int bch2_dirent_invalid(const struct bch_fs *c, struct bkey_s_c k, return -BCH_ERR_invalid_bkey; } + if (d_name.len != strnlen(d_name.name, d_name.len)) { + prt_printf(err, "dirent has stray data after name's NUL"); + return -BCH_ERR_invalid_bkey; + } + if (d_name.len == 1 && !memcmp(d_name.name, ".", 1)) { prt_printf(err, "invalid name"); return -BCH_ERR_invalid_bkey; -- 2.30.2