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[188.147.112.12]) by smtp.gmail.com with ESMTPSA id d5sm22863202wrb.28.2020.09.14.10.44.22 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 14 Sep 2020 10:44:22 -0700 (PDT) From: mateusznosek0@gmail.com To: linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org Cc: Mateusz Nosek , viro@zeniv.linux.org.uk Subject: [RFC PATCH] fs: micro-optimization remove branches by adjusting flag values Date: Mon, 14 Sep 2020 19:43:38 +0200 Message-Id: <20200914174338.9808-1-mateusznosek0@gmail.com> X-Mailer: git-send-email 2.20.1 MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Sender: linux-fsdevel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org From: Mateusz Nosek When flags A and B have equal values than the following code if(flags1 & A) flags2 |= B; is equivalent to flags2 |= (flags1 & A); The latter code should generate less instructions and be faster as one branch is omitted in it. Introduced patch changes the value of 'LOOKUP_EMPTY' and makes it equal to the value of 'AT_EMPTY_PATH'. Thanks to that, few branches can be changed in a way showed above which improves both performance and the size of the code. Signed-off-by: Mateusz Nosek --- fs/exec.c | 14 ++++++++++---- fs/fhandle.c | 4 ++-- fs/namespace.c | 4 ++-- fs/open.c | 8 ++++---- fs/stat.c | 4 ++-- fs/utimes.c | 6 +++--- include/linux/namei.h | 4 ++-- 7 files changed, 25 insertions(+), 19 deletions(-) diff --git a/fs/exec.c b/fs/exec.c index a91003e28eaa..39e1ada1ee6c 100644 --- a/fs/exec.c +++ b/fs/exec.c @@ -904,8 +904,8 @@ static struct file *do_open_execat(int fd, struct filename *name, int flags) return ERR_PTR(-EINVAL); if (flags & AT_SYMLINK_NOFOLLOW) open_exec_flags.lookup_flags &= ~LOOKUP_FOLLOW; - if (flags & AT_EMPTY_PATH) - open_exec_flags.lookup_flags |= LOOKUP_EMPTY; + BUILD_BUG_ON(AT_EMPTY_PATH != LOOKUP_EMPTY); + open_exec_flags.lookup_flags |= (flags & AT_EMPTY_PATH); file = do_filp_open(fd, name, &open_exec_flags); if (IS_ERR(file)) @@ -2176,7 +2176,10 @@ SYSCALL_DEFINE5(execveat, const char __user *const __user *, envp, int, flags) { - int lookup_flags = (flags & AT_EMPTY_PATH) ? LOOKUP_EMPTY : 0; + int lookup_flags; + + BUILD_BUG_ON(AT_EMPTY_PATH != LOOKUP_EMPTY); + lookup_flags = (flags & AT_EMPTY_PATH); return do_execveat(fd, getname_flags(filename, lookup_flags, NULL), @@ -2197,7 +2200,10 @@ COMPAT_SYSCALL_DEFINE5(execveat, int, fd, const compat_uptr_t __user *, envp, int, flags) { - int lookup_flags = (flags & AT_EMPTY_PATH) ? LOOKUP_EMPTY : 0; + int lookup_flags; + + BUILD_BUG_ON(AT_EMPTY_PATH != LOOKUP_EMPTY); + lookup_flags = (flags & AT_EMPTY_PATH); return compat_do_execveat(fd, getname_flags(filename, lookup_flags, NULL), diff --git a/fs/fhandle.c b/fs/fhandle.c index 01263ffbc4c0..579bf462bf89 100644 --- a/fs/fhandle.c +++ b/fs/fhandle.c @@ -102,8 +102,8 @@ SYSCALL_DEFINE5(name_to_handle_at, int, dfd, const char __user *, name, return -EINVAL; lookup_flags = (flag & AT_SYMLINK_FOLLOW) ? LOOKUP_FOLLOW : 0; - if (flag & AT_EMPTY_PATH) - lookup_flags |= LOOKUP_EMPTY; + BUILD_BUG_ON(AT_EMPTY_PATH != LOOKUP_EMPTY); + lookup_flags |= (flag & AT_EMPTY_PATH); err = user_path_at(dfd, name, lookup_flags, &path); if (!err) { err = do_sys_name_to_handle(&path, handle, mnt_id); diff --git a/fs/namespace.c b/fs/namespace.c index 098f981dce54..319f42d11236 100644 --- a/fs/namespace.c +++ b/fs/namespace.c @@ -2456,8 +2456,8 @@ SYSCALL_DEFINE3(open_tree, int, dfd, const char __user *, filename, unsigned, fl lookup_flags &= ~LOOKUP_AUTOMOUNT; if (flags & AT_SYMLINK_NOFOLLOW) lookup_flags &= ~LOOKUP_FOLLOW; - if (flags & AT_EMPTY_PATH) - lookup_flags |= LOOKUP_EMPTY; + BUILD_BUG_ON(AT_EMPTY_PATH != LOOKUP_EMPTY); + lookup_flags |= (flags & AT_EMPTY_PATH); if (detached && !may_mount()) return -EPERM; diff --git a/fs/open.c b/fs/open.c index 9af548fb841b..8b6fe1e89811 100644 --- a/fs/open.c +++ b/fs/open.c @@ -410,8 +410,8 @@ static long do_faccessat(int dfd, const char __user *filename, int mode, int fla if (flags & AT_SYMLINK_NOFOLLOW) lookup_flags &= ~LOOKUP_FOLLOW; - if (flags & AT_EMPTY_PATH) - lookup_flags |= LOOKUP_EMPTY; + BUILD_BUG_ON(AT_EMPTY_PATH != LOOKUP_EMPTY); + lookup_flags |= (flags & AT_EMPTY_PATH); if (!(flags & AT_EACCESS)) { old_cred = access_override_creds(); @@ -692,8 +692,8 @@ int do_fchownat(int dfd, const char __user *filename, uid_t user, gid_t group, goto out; lookup_flags = (flag & AT_SYMLINK_NOFOLLOW) ? 0 : LOOKUP_FOLLOW; - if (flag & AT_EMPTY_PATH) - lookup_flags |= LOOKUP_EMPTY; + BUILD_BUG_ON(AT_EMPTY_PATH != LOOKUP_EMPTY); + lookup_flags |= (flag & AT_EMPTY_PATH); retry: error = user_path_at(dfd, filename, lookup_flags, &path); if (error) diff --git a/fs/stat.c b/fs/stat.c index 44f8ad346db4..a9feb7a7e9ec 100644 --- a/fs/stat.c +++ b/fs/stat.c @@ -168,8 +168,8 @@ static inline unsigned vfs_stat_set_lookup_flags(unsigned *lookup_flags, *lookup_flags &= ~LOOKUP_FOLLOW; if (flags & AT_NO_AUTOMOUNT) *lookup_flags &= ~LOOKUP_AUTOMOUNT; - if (flags & AT_EMPTY_PATH) - *lookup_flags |= LOOKUP_EMPTY; + BUILD_BUG_ON(AT_EMPTY_PATH != LOOKUP_EMPTY); + *lookup_flags |= (flags & AT_EMPTY_PATH); return 0; } diff --git a/fs/utimes.c b/fs/utimes.c index fd3cc4226224..95a48dbda7e1 100644 --- a/fs/utimes.c +++ b/fs/utimes.c @@ -79,15 +79,15 @@ static int do_utimes_path(int dfd, const char __user *filename, struct timespec64 *times, int flags) { struct path path; - int lookup_flags = 0, error; + int lookup_flags, error; if (flags & ~(AT_SYMLINK_NOFOLLOW | AT_EMPTY_PATH)) return -EINVAL; + BUILD_BUG_ON(AT_EMPTY_PATH != LOOKUP_EMPTY); + lookup_flags = (flags & AT_EMPTY_PATH); if (!(flags & AT_SYMLINK_NOFOLLOW)) lookup_flags |= LOOKUP_FOLLOW; - if (flags & AT_EMPTY_PATH) - lookup_flags |= LOOKUP_EMPTY; retry: error = user_path_at(dfd, filename, lookup_flags, &path); diff --git a/include/linux/namei.h b/include/linux/namei.h index a4bb992623c4..52f8015717c0 100644 --- a/include/linux/namei.h +++ b/include/linux/namei.h @@ -21,7 +21,7 @@ enum {LAST_NORM, LAST_ROOT, LAST_DOT, LAST_DOTDOT}; #define LOOKUP_FOLLOW 0x0001 /* follow links at the end */ #define LOOKUP_DIRECTORY 0x0002 /* require a directory */ #define LOOKUP_AUTOMOUNT 0x0004 /* force terminal automount */ -#define LOOKUP_EMPTY 0x4000 /* accept empty path [user_... only] */ +#define LOOKUP_EMPTY 0x1000 /* accept empty path [user_... only], AT_EMPTY_PATH set */ #define LOOKUP_DOWN 0x8000 /* follow mounts in the starting point */ #define LOOKUP_MOUNTPOINT 0x0080 /* follow mounts in the end */ @@ -36,7 +36,7 @@ enum {LAST_NORM, LAST_ROOT, LAST_DOT, LAST_DOTDOT}; /* internal use only */ #define LOOKUP_PARENT 0x0010 -#define LOOKUP_JUMPED 0x1000 +#define LOOKUP_JUMPED 0x4000 #define LOOKUP_ROOT 0x2000 #define LOOKUP_ROOT_GRABBED 0x0008 -- 2.20.1