main/streams/plain_wrapper: skip lseek(SEEK_CUR) for newly opened files

A file that has just been opened is known to be at offset zero, and
the lseek(SEEK_CUR) system call to determine the current offset can be
skipped.

Closes #8540.

Author: MaxKellermann

NEWS

@@ -17,6 +17,7 @@ PHP                                                                        NEWS
     enums). (ilutov)
   . Fixed bug GH-8810 (Incorrect lineno in backtrace of multi-line function
     calls). (ilutov)
+  . Optimised code path for newly created file with the stream plain wrapper. (Max Kellermann)
 
 - Curl:
   . Added new constants from cURL 7.62 to 7.80. (Pierrick)

UPGRADING.INTERNALS

@@ -37,6 +37,8 @@ PHP 8.2 INTERNALS UPGRADE NOTES
   - zend_object_count_elements_t
   - zend_object_get_closure_t
   - zend_object_do_operation_t
+* Added a new zero_position argument to php_stream_fopen_from_fd_rel to reflect
+  if this a newly created file so the current file offset needs not to be checked.
 
 ========================
 2. Build system changes

main/php_streams.h

@@ -65,7 +65,7 @@ END_EXTERN_C()
 
 #define php_stream_fopen_with_path_rel(filename, mode, path, opened, options) _php_stream_fopen_with_path((filename), (mode), (path), (opened), (options) STREAMS_REL_CC)
 
-#define php_stream_fopen_from_fd_rel(fd, mode, persistent_id)	 _php_stream_fopen_from_fd((fd), (mode), (persistent_id) STREAMS_REL_CC)
+#define php_stream_fopen_from_fd_rel(fd, mode, persistent_id, zero_position)	 _php_stream_fopen_from_fd((fd), (mode), (persistent_id), (zero_position) STREAMS_REL_CC)
 #define php_stream_fopen_from_file_rel(file, mode)	 _php_stream_fopen_from_file((file), (mode) STREAMS_REL_CC)
 
 #define php_stream_fopen_from_pipe_rel(file, mode)	 _php_stream_fopen_from_pipe((file), (mode) STREAMS_REL_CC)

main/streams/php_stream_plain_wrapper.h

@@ -32,8 +32,8 @@ PHPAPI php_stream *_php_stream_fopen_with_path(const char *filename, const char
 PHPAPI php_stream *_php_stream_fopen_from_file(FILE *file, const char *mode STREAMS_DC);
 #define php_stream_fopen_from_file(file, mode)	_php_stream_fopen_from_file((file), (mode) STREAMS_CC)
 
-PHPAPI php_stream *_php_stream_fopen_from_fd(int fd, const char *mode, const char *persistent_id STREAMS_DC);
-#define php_stream_fopen_from_fd(fd, mode, persistent_id)	_php_stream_fopen_from_fd((fd), (mode), (persistent_id) STREAMS_CC)
+PHPAPI php_stream *_php_stream_fopen_from_fd(int fd, const char *mode, const char *persistent_id, bool zero_position STREAMS_DC);
+#define php_stream_fopen_from_fd(fd, mode, persistent_id)	_php_stream_fopen_from_fd((fd), (mode), (persistent_id), false STREAMS_CC)
 
 PHPAPI php_stream *_php_stream_fopen_from_pipe(FILE *file, const char *mode STREAMS_DC);
 #define php_stream_fopen_from_pipe(file, mode)	_php_stream_fopen_from_pipe((file), (mode) STREAMS_CC)

main/streams/plain_wrapper.c

@@ -274,7 +274,7 @@ static void detect_is_seekable(php_stdio_stream_data *self) {
 #endif
 }
 
-PHPAPI php_stream *_php_stream_fopen_from_fd(int fd, const char *mode, const char *persistent_id STREAMS_DC)
+PHPAPI php_stream *_php_stream_fopen_from_fd(int fd, const char *mode, const char *persistent_id, bool zero_position STREAMS_DC)
 {
 	php_stream *stream = php_stream_fopen_from_fd_int_rel(fd, mode, persistent_id);
 
@@ -285,6 +285,9 @@ PHPAPI php_stream *_php_stream_fopen_from_fd(int fd, const char *mode, const cha
 		if (!self->is_seekable) {
 			stream->flags |= PHP_STREAM_FLAG_NO_SEEK;
 			stream->position = -1;
+		} else if (zero_position) {
+			ZEND_ASSERT(zend_lseek(self->fd, 0, SEEK_CUR) == 0);
+			stream->position = 0;
 		} else {
 			stream->position = zend_lseek(self->fd, 0, SEEK_CUR);
 #ifdef ESPIPE
@@ -1141,7 +1144,12 @@ PHPAPI php_stream *_php_stream_fopen(const char *filename, const char *mode, zen
 		if (options & STREAM_OPEN_FOR_INCLUDE) {
 			ret = php_stream_fopen_from_fd_int_rel(fd, mode, persistent_id);
 		} else {
-			ret = php_stream_fopen_from_fd_rel(fd, mode, persistent_id);
+			/* skip the lseek(SEEK_CUR) system call to
+			 * determine the current offset because we
+			 * know newly opened files are at offset zero
+			 * (unless the file has been opened in
+			 * O_APPEND mode) */
+			ret = php_stream_fopen_from_fd_rel(fd, mode, persistent_id, (open_flags & O_APPEND) == 0);
 		}
 
 		if (ret)	{