fs: fix standard zero, full devices

The standard devices are currently broken since they have
the size ~0. As now files use loff_t as file size which is a signed
type the read implementation gets confused and now returns -1.

The current implementation also has the (somewhat theorical) problem
that we do not have real streaming devices, so /dev/zero went out
of zeroes after reading 4GB (or now LLONG_MAX).

This patch introduces a new cdev flag DEVFS_IS_CHARACTER_DEV and a new
file size flag FILE_SIZE_STREAM which makes it possible to create
real stream devices instead.

Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>

2 files changed, 6 insertions, 5 deletions

diff --git a/fs/devfs.c b/fs/devfs.c
index ea8b250a68..fccf25a721 100644
--- a/fs/devfs.c
+++ b/fs/devfs.c
@@ -121,7 +121,8 @@ static int devfs_open(struct device_d *_dev, FILE *f, const char *filename)
 	if (!cdev)
 		return -ENOENT;
 
-	f->size = cdev->size;
+	f->size = cdev->flags & DEVFS_IS_CHARACTER_DEV ?
+			FILE_SIZE_STREAM : cdev->size;
 	f->inode = cdev;
 
 	if (cdev->ops->open) {
diff --git a/fs/fs.c b/fs/fs.c
index 1774fb719f..0b376a544b 100644
--- a/fs/fs.c
+++ b/fs/fs.c
@@ -643,7 +643,7 @@ int read(int fd, void *buf, size_t count)
 
 	fsdrv = dev_to_fs_driver(dev);
 
-	if (f->pos + count > f->size)
+	if (f->size != FILE_SIZE_STREAM && f->pos + count > f->size)
 		count = f->size - f->pos;
 
 	if (!count)
@@ -672,7 +672,7 @@ ssize_t write(int fd, const void *buf, size_t count)
 	dev = f->dev;
 
 	fsdrv = dev_to_fs_driver(dev);
-	if (f->pos + count > f->size) {
+	if (f->size != FILE_SIZE_STREAM && f->pos + count > f->size) {
 		ret = fsdrv->truncate(dev, f, f->pos + count);
 		if (ret) {
 			if (ret != -ENOSPC)
@@ -740,12 +740,12 @@ loff_t lseek(int fildes, loff_t offset, int whence)
 
 	switch (whence) {
 	case SEEK_SET:
-		if (offset > f->size)
+		if (f->size != FILE_SIZE_STREAM && offset > f->size)
 			goto out;
 		pos = offset;
 		break;
 	case SEEK_CUR:
-		if (offset + f->pos > f->size)
+		if (f->size != FILE_SIZE_STREAM && offset + f->pos > f->size)
 			goto out;
 		pos = f->pos + offset;
 		break;