[PATCH RFC 2/8] fs: always get the file size in _fs_read()

[Qu Wenruo <wqu@suse.com>]

For _fs_read(), @len == 0 means we read the whole file.
And we just pass @len == 0 to make each filesystem to handle it.

In fact we have info->size() call to properly get the filesize.

So we can not only call info->size() to grab the file_size for len == 0
case, but also detect invalid @len (e.g. @len > file_size) in advance or
truncate @len.

This behavior also allows us to handle unaligned better in the incoming
patches.

Signed-off-by: Qu Wenruo <wqu@suse.com>
---
 fs/fs.c | 25 +++++++++++++++++++++----
 1 file changed, 21 insertions(+), 4 deletions(-)

diff --git a/fs/fs.c b/fs/fs.c
index 6de1a3eb6d5d..d992cdd6d650 100644
--- a/fs/fs.c
+++ b/fs/fs.c
@@ -579,6 +579,7 @@ static int _fs_read(const char *filename, ulong addr, loff_t offset, loff_t len,
 {
 	struct fstype_info *info = fs_get_info(fs_type);
 	void *buf;
+	loff_t file_size;
 	int ret;
 
 #ifdef CONFIG_LMB
@@ -589,10 +590,26 @@ static int _fs_read(const char *filename, ulong addr, loff_t offset, loff_t len,
 	}
 #endif
 
-	/*
-	 * We don't actually know how many bytes are being read, since len==0
-	 * means read the whole file.
-	 */
+	ret = info->size(filename, &file_size);
+	if (ret < 0) {
+		log_err("** Unable to get file size for %s, %d **\n",
+				filename, ret);
+		return ret;
+	}
+	if (offset >= file_size) {
+		log_err(
+		"** Invalid offset, offset (%llu) >= file size (%llu)\n",
+			offset, file_size);
+		return -EINVAL;
+
+	}
+	if (len == 0 || offset + len > file_size) {
+		if (len > file_size)
+			log_info(
+	"** Truncate read length from %llu to %llu, as file size is %llu **\n",
+				 len, file_size, file_size);
+		len = file_size - offset;
+	}
 	buf = map_sysmem(addr, len);
 	ret = info->read(filename, buf, offset, len, actread);
 	unmap_sysmem(buf);
-- 
2.36.1