tftp: implement forward seeking

Just abuse tftp_read to step forward.

Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>

1 files changed, 26 insertions, 1 deletions

diff --git a/fs/tftp.c b/fs/tftp.c
index ebb81e9fca..847921aa56 100644
--- a/fs/tftp.c
+++ b/fs/tftp.c
@@ -589,7 +589,32 @@ static int tftp_read(struct device_d *dev, FILE *f, void *buf, size_t insize)
 
 static loff_t tftp_lseek(struct device_d *dev, FILE *f, loff_t pos)
 {
-	/* not implemented in tftp protocol */
+	/* We cannot seek backwards without reloading or caching the file */
+	if (pos >= f->pos) {
+		loff_t ret;
+		char *buf = xmalloc(1024);
+
+		while (pos > f->pos) {
+			size_t len = min_t(size_t, 1024, pos - f->pos);
+
+			ret = tftp_read(dev, f, buf, len);
+
+			if (!ret)
+				/* EOF, so the desired pos is invalid. */
+				ret = -EINVAL;
+			if (ret < 0)
+				goto out_free;
+
+			f->pos += ret;
+		}
+
+		ret = pos;
+
+out_free:
+		free(buf);
+		return ret;
+	}
+
 	return -ENOSYS;
 }