VFS: Implement pread() and pwrite()

Closes https://github.com/espressif/esp-idf/issues/3515

components/vfs/include/esp_vfs.h

@@ -112,6 +112,14 @@ typedef struct
         ssize_t (*read_p)(void* ctx, int fd, void * dst, size_t size);
         ssize_t (*read)(int fd, void * dst, size_t size);
     };
+    union {
+        ssize_t (*pread_p)(void *ctx, int fd, void * dst, size_t size, off_t offset);
+        ssize_t (*pread)(int fd, void * dst, size_t size, off_t offset);
+    };
+    union {
+        ssize_t (*pwrite_p)(void *ctx, int fd, const void *src, size_t size, off_t offset);
+        ssize_t (*pwrite)(int fd, const void *src, size_t size, off_t offset);
+    };
     union {
         int (*open_p)(void* ctx, const char * path, int flags, int mode);
         int (*open)(const char * path, int flags, int mode);
@@ -414,6 +422,35 @@ void esp_vfs_select_triggered_isr(esp_vfs_select_sem_t sem, BaseType_t *woken);
  */
 int esp_vfs_poll(struct pollfd *fds, nfds_t nfds, int timeout);
 
+
+/**
+ *
+ * @brief Implements the VFS layer of POSIX pread()
+ *
+ * @param fd         File descriptor used for read
+ * @param dst        Pointer to the buffer where the output will be written
+ * @param size       Number of bytes to be read
+ * @param offset     Starting offset of the read
+ *
+ * @return           A positive return value indicates the number of bytes read. -1 is return on failure and errno is
+ *                   set accordingly.
+ */
+ssize_t esp_vfs_pread(int fd, void *dst, size_t size, off_t offset);
+
+/**
+ *
+ * @brief Implements the VFS layer of POSIX pwrite()
+ *
+ * @param fd         File descriptor used for write
+ * @param src        Pointer to the buffer from where the output will be read
+ * @param size       Number of bytes to write
+ * @param offset     Starting offset of the write
+ *
+ * @return           A positive return value indicates the number of bytes written. -1 is return on failure and errno is
+ *                   set accordingly.
+ */
+ssize_t esp_vfs_pwrite(int fd, const void *src, size_t size, off_t offset);
+
 #ifdef __cplusplus
 } // extern "C"
 #endif

components/vfs/vfs.c

@@ -447,6 +447,33 @@ ssize_t esp_vfs_read(struct _reent *r, int fd, void * dst, size_t size)
     return ret;
 }
 
+ssize_t esp_vfs_pread(int fd, void *dst, size_t size, off_t offset)
+{
+    struct _reent *r = __getreent();
+    const vfs_entry_t* vfs = get_vfs_for_fd(fd);
+    const int local_fd = get_local_fd(vfs, fd);
+    if (vfs == NULL || local_fd < 0) {
+        __errno_r(r) = EBADF;
+        return -1;
+    }
+    ssize_t ret;
+    CHECK_AND_CALL(ret, r, vfs, pread, local_fd, dst, size, offset);
+    return ret;
+}
+
+ssize_t esp_vfs_pwrite(int fd, const void *src, size_t size, off_t offset)
+{
+    struct _reent *r = __getreent();
+    const vfs_entry_t* vfs = get_vfs_for_fd(fd);
+    const int local_fd = get_local_fd(vfs, fd);
+    if (vfs == NULL || local_fd < 0) {
+        __errno_r(r) = EBADF;
+        return -1;
+    }
+    ssize_t ret;
+    CHECK_AND_CALL(ret, r, vfs, pwrite, local_fd, src, size, offset);
+    return ret;
+}
 
 int esp_vfs_close(struct _reent *r, int fd)
 {