sys/vfs_util: add VFS helper functions

sys/Makefile.dep

@@ -559,6 +559,10 @@ ifneq (,$(filter vfs_default,$(USEMODULE)))
   DEFAULT_MODULE += vfs_auto_mount
 endif
 
+ifneq (,$(filter vfs_util,$(USEMODULE)))
+  USEMODULE += vfs
+endif
+
 ifneq (,$(filter vfs,$(USEMODULE)))
   USEMODULE += posix_headers
   ifeq (native, $(BOARD))

sys/include/vfs.h

@@ -794,6 +794,9 @@ int vfs_open(const char *name, int flags, mode_t mode);
  *
  * @return number of bytes read on success
  * @return <0 on error
+ *
+ * For simple cases of only a single read from a file, the @ref
+ * vfs_file_to_buffer function can be used.
  */
 ssize_t vfs_read(int fd, void *dest, size_t count);
 
@@ -806,6 +809,9 @@ ssize_t vfs_read(int fd, void *dest, size_t count);
  *
  * @return number of bytes written on success
  * @return <0 on error
+ *
+ * For simple cases of only a single write to a file, the @ref
+ * vfs_file_from_buffer function can be used.
  */
 ssize_t vfs_write(int fd, const void *src, size_t count);
 

sys/include/vfs_util.h

@@ -0,0 +1,59 @@
+/*
+ * Copyright (C) 2021 ML!PA Consulting GmbH
+ *
+ * This file is subject to the terms and conditions of the GNU Lesser General
+ * Public License v2.1. See the file LICENSE in the top level directory for more
+ * details.
+ */
+
+/**
+ * @defgroup    sys_vfs_util    VFS helper functions
+ * @ingroup     sys_vfs
+ * @{
+ *
+ * @file
+ * @brief       VFS helper functions
+ *
+ * @author      Benjamin Valentin <benjamin.valentin@ml-pa.com>
+ */
+
+#ifndef VFS_UTIL_H
+#define VFS_UTIL_H
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+/**
+ * @brief   Writes the content of a buffer to a file
+ *          If the file already exists, it will be overwritten.
+ *
+ * @param[in]  file     Destination file path
+ * @param[in]  buf      Source buffer
+ * @param[in]  len      Buffer size
+ *
+ * @return  0 on success
+ * @return  negative error from @ref vfs_open, @ref vfs_write
+ */
+int vfs_file_from_buffer(const char *file, const void *buf, size_t len);
+
+/**
+ * @brief   Reads the content of a file to a buffer
+ *
+ * @param[in]  file     Source file path
+ * @param[out] buf      Destination buffer
+ * @param[in]  len      Buffer size
+ *
+ * @return  number of bytes read on success
+ * @return  -ENOSPC if the file was read successfully but is larger than
+ *          the provided buffer. Only the first @p len bytes were read.
+ * @return  negative error from @ref vfs_open, @ref vfs_read
+ */
+int vfs_file_to_buffer(const char* file, void* buf, size_t len);
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif /* VFS_UTIL_H */
+/** @} */

sys/vfs_util/Makefile

@@ -0,0 +1 @@
+include $(RIOTBASE)/Makefile.base

sys/vfs_util/vfs_util.c

@@ -0,0 +1,81 @@
+/*
+ * Copyright (C) 2021 Benjamin Valentin
+ *
+ * This file is subject to the terms and conditions of the GNU Lesser
+ * General Public License v2.1. See the file LICENSE in the top level
+ * directory for more details.
+ */
+
+/**
+ * @ingroup     sys_vfs_util
+ * @{
+ * @file
+ * @brief   VFS layer helper functions
+ * @author  Benjamin Valentin <benjamin.valentin@ml-pa.com>
+ * @}
+ */
+
+#include <fcntl.h>
+#include <string.h>
+#include <errno.h>
+
+#include "vfs.h"
+#include "vfs_util.h"
+
+#define ENABLE_DEBUG 0
+#include "debug.h"
+
+int vfs_file_from_buffer(const char *file, const void *buf, size_t len)
+{
+    int res, fd = vfs_open(file, O_CREAT | O_TRUNC | O_WRONLY, 0644);
+
+    if (fd < 0) {
+        DEBUG("can't open %s for writing\n", file);
+        return fd;
+    }
+
+    res = vfs_write(fd, buf, len);
+    vfs_close(fd);
+
+    if (res) {
+        return res;
+    }
+
+    return 0;
+}
+
+int vfs_file_to_buffer(const char* file, void* buf, size_t len)
+{
+    int res, fd = vfs_open(file, O_RDONLY, 0);
+
+    if (fd < 0) {
+        DEBUG("can't open %s for reading\n", file);
+        return fd;
+    }
+
+    res = vfs_read(fd, buf, len);
+
+    /* ENOSPC is used to signal truncation */
+    /* Just for future proofing - this error code is not returned by any fs in the read path. */
+    if (res == -ENOSPC) {
+        DEBUG("read returned -ENOSPC\n");
+        res = -ENOMEM;
+    }
+
+    if (res > 0) {
+        if (res < (int)len) {
+            /* fill remaining buffer with 0 */
+            memset((char *)buf + res, 0, len - res);
+        } else {
+            /* check if there are more bytes in the file */
+            char c;
+            if (vfs_read(fd, &c, sizeof(c)) > 0) {
+                res = -ENOSPC;
+            }
+        }
+    }
+
+    vfs_close(fd);
+
+    return res;
+}