Make evbuffer_file_segment_types adaptable

Instead of having a file segment born as one type and stay that way
forever, let them start out unmapped, but map themselves as needed
if they need to get written out on a non-drains_to_fd evbuffer.

buffer.c

@@ -149,6 +149,8 @@ static struct evbuffer_chain *evbuffer_expand_singlechain(struct evbuffer *buf,
     size_t datlen);
 static int evbuffer_ptr_subtract(struct evbuffer *buf, struct evbuffer_ptr *pos,
     size_t howfar);
+static int evbuffer_file_segment_materialize(struct evbuffer_file_segment *seg);
+
 
 static struct evbuffer_chain *
 evbuffer_chain_new(size_t size)
@@ -204,7 +206,7 @@ evbuffer_chain_free(struct evbuffer_chain *chain)
 			    chain);
 		if (info->segment) {
 #ifdef _WIN32
-			if (info->segment->type == EVBUF_FS_MMAP)
+			if (info->segment->is_mapping)
 				UnmapViewOfFile(chain->buffer);
 #endif
 			evbuffer_file_segment_free(info->segment);
@@ -2680,6 +2682,7 @@ evbuffer_file_segment_new(
 	seg->refcnt = 1;
 	seg->fd = fd;
 	seg->flags = flags;
+	seg->file_offset = offset;
 
 #ifdef _WIN32
 #define lseek _lseeki64
@@ -2696,11 +2699,37 @@ evbuffer_file_segment_new(
 
 #if defined(USE_SENDFILE)
 	if (!(flags & EVBUF_FS_DISABLE_SENDFILE)) {
-		seg->offset = offset;
+		seg->can_sendfile = 1;
-		seg->type = EVBUF_FS_SENDFILE;
 		goto done;
 	}
 #endif
+
+	if (evbuffer_file_segment_materialize(seg)<0)
+		goto err;
+
+done:
+	if (!(flags & EVBUF_FS_DISABLE_LOCKING)) {
+		EVTHREAD_ALLOC_LOCK(seg->lock, 0);
+	}
+	return seg;
+err:
+	mm_free(seg);
+	return NULL;
+}
+
+/* DOCDOC */
+/* Requires lock */
+static int
+evbuffer_file_segment_materialize(struct evbuffer_file_segment *seg)
+{
+	const unsigned flags = seg->flags;
+	const int fd = seg->fd;
+	const ev_off_t length = seg->length;
+	const ev_off_t offset = seg->file_offset;
+
+	if (seg->contents)
+		return 0; /* already materialized */
+
 #if defined(_EVENT_HAVE_MMAP)
 	if (!(flags & EVBUF_FS_DISABLE_MMAP)) {
 		off_t offset_rounded = 0, offset_leftover = 0;
@@ -2736,8 +2765,8 @@ evbuffer_file_segment_new(
 		} else {
 			seg->mapping = mapped;
 			seg->contents = (char*)mapped+offset_leftover;
-			seg->offset = 0;
+			seg->mmap_offset = 0;
-			seg->type = EVBUF_FS_MMAP;
+			seg->is_mapping = 1;
 			goto done;
 		}
 	}
@@ -2754,8 +2783,8 @@ evbuffer_file_segment_new(
 		    NULL);
 		if (m != INVALID_HANDLE_VALUE) { /* Does h leak? */
 			seg->mapping_handle = m;
-			seg->offset = offset;
+			seg->mmap_offset = offset;
-			seg->type = EVBUF_FS_MMAP;
+			seg->is_mapping = 1;
 			goto done;
 		}
 	}
@@ -2795,17 +2824,12 @@ evbuffer_file_segment_new(
 		}
 
 		seg->contents = mem;
-		seg->type = EVBUF_FS_IO;
 	}
 
 done:
-	if (!(flags & EVBUF_FS_DISABLE_LOCKING)) {
+	return 0;
-		EVTHREAD_ALLOC_LOCK(seg->lock, 0);
-	}
-	return seg;
 err:
-	mm_free(seg);
+	return -1;
-	return NULL;
 }
 
 void
@@ -2819,17 +2843,14 @@ evbuffer_file_segment_free(struct evbuffer_file_segment *seg)
 		return;
 	EVUTIL_ASSERT(refcnt == 0);
 
-	if (seg->type == EVBUF_FS_SENDFILE) {
+	if (seg->is_mapping) {
-		;
-	} else if (seg->type == EVBUF_FS_MMAP) {
 #ifdef _WIN32
 		CloseHandle(seg->mapping_handle);
 #elif defined (_EVENT_HAVE_MMAP)
 		if (munmap(seg->mapping, seg->length) == -1)
 			event_warn("%s: munmap failed", __func__);
 #endif
-	} else {
+	} else if (seg->contents) {
-		EVUTIL_ASSERT(seg->type == EVBUF_FS_IO);
 		mm_free(seg->contents);
 	}
 
@@ -2847,12 +2868,23 @@ evbuffer_add_file_segment(struct evbuffer *buf,
 {
 	struct evbuffer_chain *chain;
 	struct evbuffer_chain_file_segment *extra;
-
+	int can_use_sendfile = 0;
-	EVLOCK_LOCK(seg->lock, 0);
-	++seg->refcnt;
-	EVLOCK_UNLOCK(seg->lock, 0);
 
 	EVBUFFER_LOCK(buf);
+	EVLOCK_LOCK(seg->lock, 0);
+	if (buf->flags & EVBUFFER_FLAG_DRAINS_TO_FD) {
+		can_use_sendfile = 1;
+	} else {
+		if (!seg->contents) {
+			if (evbuffer_file_segment_materialize(seg)<0) {
+				EVLOCK_UNLOCK(seg->lock, 0);
+				EVBUFFER_UNLOCK(buf);
+				return -1;
+			}
+		}
+	}
+	++seg->refcnt;
+	EVLOCK_UNLOCK(seg->lock, 0);
 
 	if (buf->freeze_end)
 		goto err;
@@ -2873,14 +2905,14 @@ evbuffer_add_file_segment(struct evbuffer *buf,
 	extra = EVBUFFER_CHAIN_EXTRA(struct evbuffer_chain_file_segment, chain);
 
 	chain->flags |= EVBUFFER_IMMUTABLE|EVBUFFER_FILESEGMENT;
-	if (seg->type == EVBUF_FS_SENDFILE) {
+	if (can_use_sendfile && seg->can_sendfile) {
 		chain->flags |= EVBUFFER_SENDFILE;
-		chain->misalign = seg->offset + offset;
+		chain->misalign = seg->file_offset + offset;
 		chain->off = length;
 		chain->buffer_len = chain->misalign + length;
-	} else if (seg->type == EVBUF_FS_MMAP) {
+	} else if (seg->is_mapping) {
 #ifdef _WIN32
-		ev_uint64_t total_offset = seg->offset+offset;
+		ev_uint64_t total_offset = seg->mmap_offset+offset;
 		ev_uint64_t offset_rounded=0, offset_remaining=0;
 		LPVOID data;
 		if (total_offset) {
@@ -2910,7 +2942,6 @@ evbuffer_add_file_segment(struct evbuffer *buf,
 		chain->off = length;
 #endif
 	} else {
-		EVUTIL_ASSERT(seg->type == EVBUF_FS_IO);
 		chain->buffer = (unsigned char*)(seg->contents + offset);
 		chain->buffer_len = length;
 		chain->off = length;

evbuffer-internal.h

@@ -220,7 +220,8 @@ struct evbuffer_file_segment {
 	unsigned flags; /**< combination of EVBUF_FS_* flags  */
 
 	/** What kind of file segment is this? */
-	enum {EVBUF_FS_MMAP, EVBUF_FS_SENDFILE, EVBUF_FS_IO} type;
+	unsigned can_sendfile : 1;
+	unsigned is_mapping : 1;
 
 	/** The fd that we read the data from. */
 	int fd;
@@ -233,11 +234,11 @@ struct evbuffer_file_segment {
 	/** If we're using mmap or IO, this is the content of the file
 	 * segment. */
 	char *contents;
+	/** Position of this segment within the file. */
+	ev_off_t file_offset;
 	/** If we're using mmap, this is the offset within 'mapping' where
-	 * this data segment begins.  If we're using sendfile, this is the
+	 * this data segment begins. */
-	 * offset within the file where this data begins.  If we're using IO,
+	ev_off_t mmap_offset;
-	 * this is 0. */
-	ev_off_t offset;
 	/** The length of this segment. */
 	ev_off_t length;
 };

test/regress_buffer.c

@@ -652,7 +652,7 @@ test_evbuffer_add_file(void *ptr)
 	size_t datalen, expect_len;
 	const char *compare;
 	int fd = -1;
-	int want_type = 0;
+	int want_ismapping = -1, want_cansendfile = -1;
 	unsigned flags = 0;
 	int use_segment = 1, use_bigfile = 0, map_from_offset = 0,
 	    view_from_offset = 0;
@@ -692,17 +692,20 @@ test_evbuffer_add_file(void *ptr)
 		/* If sendfile is set, we try to use a sendfile/splice style
 		 * backend. */
 		flags = EVBUF_FS_DISABLE_MMAP;
-		want_type = EVBUF_FS_SENDFILE;
+		want_cansendfile = 1;
+		want_ismapping = 0;
 	} else if (strstr(impl, "mmap")) {
 		/* If sendfile is set, we try to use a mmap/CreateFileMapping
 		 * style backend. */
 		flags = EVBUF_FS_DISABLE_SENDFILE;
-		want_type = EVBUF_FS_MMAP;
+		want_ismapping = 1;
+		want_cansendfile = 0;
 	} else if (strstr(impl, "linear")) {
 		/* If linear is set, we try to use a read-the-whole-thing
 		 * backend. */
 		flags = EVBUF_FS_DISABLE_SENDFILE|EVBUF_FS_DISABLE_MMAP;
-		want_type = EVBUF_FS_IO;
+		want_ismapping = 0;
+		want_cansendfile = 0;
 	} else if (strstr(impl, "default")) {
 		/* The caller doesn't care which backend we use. */
 		;
@@ -747,8 +750,14 @@ test_evbuffer_add_file(void *ptr)
 		seg = evbuffer_file_segment_new(fd, starting_offset,
 		    mapping_len, flags);
 		tt_assert(seg);
-		if ((int)seg->type != (int)want_type)
+		if (want_ismapping >= 0) {
-			tt_skip();
+			if (seg->is_mapping != (unsigned)want_ismapping)
+				tt_skip();
+		}
+		if (want_cansendfile >= 0) {
+			if (seg->can_sendfile != (unsigned)want_cansendfile)
+				tt_skip();
+		}
 	}
 
 	/* Say that it drains to a fd so that we can use sendfile. */