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Subject[RFC PATCH] seq_puts: Optimize seq_puts for compile-time known constant string lengths
Date
Use a macro to call seq_write for constant strings and seq_puts for
possible variable length char * uses.

Parenthesize seq_puts to avoid recursive macro expansions.

Code size is slightly larger per call, but a runtime calculation
of strlen(string) is avoided.

Signed-off-by: Joe Perches <joe@perches.com>
---
fs/seq_file.c | 2 +-
include/linux/seq_file.h | 13 ++++++++++++-
2 files changed, 13 insertions(+), 2 deletions(-)

diff --git a/fs/seq_file.c b/fs/seq_file.c
index 19f532e..3e50e1f 100644
--- a/fs/seq_file.c
+++ b/fs/seq_file.c
@@ -661,7 +661,7 @@ void seq_putc(struct seq_file *m, char c)
}
EXPORT_SYMBOL(seq_putc);

-void seq_puts(struct seq_file *m, const char *s)
+void (seq_puts)(struct seq_file *m, const char *s)
{
int len = strlen(s);

diff --git a/include/linux/seq_file.h b/include/linux/seq_file.h
index f3d45dd..672f4c0 100644
--- a/include/linux/seq_file.h
+++ b/include/linux/seq_file.h
@@ -116,7 +116,18 @@ void seq_vprintf(struct seq_file *m, const char *fmt, va_list args);
__printf(2, 3)
void seq_printf(struct seq_file *m, const char *fmt, ...);
void seq_putc(struct seq_file *m, char c);
-void seq_puts(struct seq_file *m, const char *s);
+
+void (seq_puts)(struct seq_file *m, const char *s);
+/* Hack to allow constant strings to use compile-time calculated lengths */
+# define seq_puts(seq, string) \
+do { \
+ if (__builtin_constant_p(string) && \
+ (sizeof(string) != sizeof(const char *))) \
+ seq_write(seq, string, sizeof(string) - 1); \
+ else \
+ (seq_puts)(seq, string); \
+} while (0)
+
void seq_put_decimal_ull(struct seq_file *m, char delimiter,
unsigned long long num);
void seq_put_decimal_ll(struct seq_file *m, char delimiter, long long num);
--
2.8.0.rc4.16.g56331f8
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