text: overhaul file load implementation

Files smaller than 8M are now copied into an internal buffer
upon load. Thus they can be safely truncated. Larger files are
memory mapped and use the file/virtual memory system as caching
layer. Hence truncating them will corrupt the file content.
Eventually the resulting SIGBUS should be handled gracefully.

1 files changed, 34 insertions, 3 deletions

diff --git a/text.c b/text.c
index 6457cff..e013979 100644
--- a/text.c
+++ b/text.c
@@ -35,6 +35,10 @@
 #include "util.h"
 
 #define BUFFER_SIZE (1 << 20)
+/* Files smaller than this value are copied on load, larger ones are mmap(2)-ed
+ * directely. Hence the former can be truncated, while doing so on the latter
+ * results in havoc. */
+#define BUFFER_MMAP_SIZE (1 << 23)
 
 struct Regex {
 	const char *string;
@@ -136,6 +140,7 @@ struct Text {
 
 /* buffer management */
 static Buffer *buffer_alloc(Text *txt, size_t size);
+static Buffer *buffer_read(Text *txt, size_t size, int fd);
 static Buffer *buffer_mmap(Text *txt, size_t size, int fd, off_t offset);
 static void buffer_free(Buffer *buf);
 static bool buffer_capacity(Buffer *buf, size_t len);
@@ -203,6 +208,27 @@ static Buffer *buffer_alloc(Text *txt, size_t size) {
 	return buf;
 }
 
+static Buffer *buffer_read(Text *txt, size_t size, int fd) {
+	Buffer *buf = buffer_alloc(txt, size);
+	if (!buf)
+		return NULL;
+	while (size > 0) {
+		char data[4096];
+		ssize_t len = read(fd, data, MIN(sizeof(data), size));
+		if (len == -1) {
+			txt->buffers = buf->next;
+			buffer_free(buf);
+			return NULL;
+		} else if (len == 0) {
+			break;
+		} else {
+			buffer_append(buf, data, len);
+			size -= len;
+		}
+	}
+	return buf;
+}
+
 static Buffer *buffer_mmap(Text *txt, size_t size, int fd, off_t offset) {
 	Buffer *buf = calloc(1, sizeof(Buffer));
 	if (!buf)
@@ -993,15 +1019,20 @@ Text *text_load(const char *filename) {
 			goto out;
 		}
 		// XXX: use lseek(fd, 0, SEEK_END); instead?
-		if (!(txt->buf = buffer_mmap(txt, txt->info.st_size, txt->fd, 0)))
+		size_t size = txt->info.st_size;
+		if (size < BUFFER_MMAP_SIZE)
+			txt->buf = buffer_read(txt, size, txt->fd);
+		else
+			txt->buf = buffer_mmap(txt, size, txt->fd, 0);
+		if (!txt->buf)
 			goto out;
 		Piece *p = piece_alloc(txt);
 		if (!p)
 			goto out;
 		piece_init(&txt->begin, NULL, p, NULL, 0);
-		piece_init(p, &txt->begin, &txt->end, txt->buf->data, txt->buf->size);
+		piece_init(p, &txt->begin, &txt->end, txt->buf->data, txt->buf->len);
 		piece_init(&txt->end, p, NULL, NULL, 0);
-		txt->size = txt->buf->size;
+		txt->size = txt->buf->len;
 	}
 	/* write an empty action */
 	change_alloc(txt, EPOS);