sandbox: implement exists() function

This hooks into the generic "file exists" support added in an earlier
patch, and provides an implementation for the sandbox test environment.

Signed-off-by: Stephen Warren <swarren@nvidia.com>
Acked-by: Simon Glass <sjg@chromium.org>

fs/fs.c

@@ -114,7 +114,7 @@ static struct fstype_info fstypes[] = {
 		.probe = sandbox_fs_set_blk_dev,
 		.close = sandbox_fs_close,
 		.ls = sandbox_fs_ls,
-		.exists = fs_exists_unsupported,
+		.exists = sandbox_fs_exists,
 		.read = fs_read_sandbox,
 		.write = fs_write_sandbox,
 	},

fs/sandbox/sandboxfs.c

@@ -72,6 +72,14 @@ int sandbox_fs_ls(const char *dirname)
 	return 0;
 }
 
+int sandbox_fs_exists(const char *filename)
+{
+	ssize_t sz;
+
+	sz = os_get_filesize(filename);
+	return sz >= 0;
+}
+
 void sandbox_fs_close(void)
 {
 }

include/sandboxfs.h

@@ -25,6 +25,7 @@ long sandbox_fs_read_at(const char *filename, unsigned long pos,
 
 void sandbox_fs_close(void);
 int sandbox_fs_ls(const char *dirname);
+int sandbox_fs_exists(const char *filename);
 int fs_read_sandbox(const char *filename, void *buf, int offset, int len);
 int fs_write_sandbox(const char *filename, void *buf, int offset, int len);