libc: add support for custom streams with fopencookie()

This commit adds support for custom stream via fopencookie function.
The function allows the programmer the create his own custom stream
for IO operations and hook his custom functions to it.

This is a non POSIX interface defined in Standard C library and implemented
according to it. The only difference is in usage of off_t instead of
off64_t. Programmer can use 64 bits offset if CONFIG_FS_LARGEFILE is
enabled. In that case off_t is defined as int64_t (int32_t otherwise).

Field fs_fd is removed from file_struct and fs_cookie is used instead
as a shared variable for file descriptor or user defined cookie.

The interface will be useful for future fmemopen implementation.

Signed-off-by: Michal Lenc <[email protected]>

fs/vfs/fs_fdopen.c

@@ -111,7 +111,7 @@ static inline int fs_checkfd(FAR struct tcb_s *tcb, int fd, int oflags)
  *
  ****************************************************************************/
 
-int fs_fdopen(int fd, int oflags, FAR struct tcb_s *tcb,
+int fs_fdopen(int fd, int cookie, int oflags, FAR struct tcb_s *tcb,
               FAR struct file_struct **filep)
 {
   FAR struct streamlist *slist;
@@ -120,7 +120,7 @@ int fs_fdopen(int fd, int oflags, FAR struct tcb_s *tcb,
 
   /* Check input parameters */
 
-  if (fd < 0)
+  if (fd < 0 && cookie == 0)
     {
       ret = -EBADF;
       goto errout;
@@ -158,7 +158,7 @@ int fs_fdopen(int fd, int oflags, FAR struct tcb_s *tcb,
 
   /* Allocate FILE structure */
 
-  if (fd >= 3)
+  if (fd >= 3 || cookie == 1)
     {
       stream = group_zalloc(tcb->group, sizeof(FILE));
       if (stream == NULL)
@@ -221,8 +221,11 @@ int fs_fdopen(int fd, int oflags, FAR struct tcb_s *tcb,
    * file descriptor locks this stream.
    */
 
-  stream->fs_fd       = fd;
-  stream->fs_oflags   = oflags;
+  stream->fs_cookie    = (FAR void *)(intptr_t)fd;
+  stream->fs_oflags    = oflags;
+#ifdef CONFIG_FDSAN
+  stream->fs_hascookie = cookie;
+#endif
 
   if (filep != NULL)
     {

include/nuttx/fs/fs.h

@@ -426,6 +426,31 @@ struct inode
 
 #define FSNODE_SIZE(n) (sizeof(struct inode) + (n))
 
+/* Definitions for custom stream operations with fopencookie. The
+ * implementation is as defined in Standard C library (libc). The only
+ * difference is that we use off_t instead of off64_t. This means
+ * off_t is int64_t if CONFIG_FS_LARGEFILE is defined and int32_t if not.
+ *
+ * These callbacks can either lead to custom functions if fopencookie is used
+ * or to standard file system functions if not.
+ */
+
+typedef CODE ssize_t cookie_read_function_t(void *cookie, char *buf,
+                                            size_t size);
+typedef CODE ssize_t cookie_write_function_t(void *cookie, const char *buf,
+                                             size_t size);
+typedef CODE off_t cookie_seek_function_t(void *cookie, off_t *offset,
+                                     int whence);
+typedef CODE int cookie_close_function_t(void *cookie);
+
+typedef struct cookie_io_functions_t
+{
+  FAR cookie_read_function_t *read;
+  FAR cookie_write_function_t *write;
+  FAR cookie_seek_function_t *seek;
+  FAR cookie_close_function_t *close;
+} cookie_io_functions_t;
+
 /* This is the underlying representation of an open file.  A file
  * descriptor is an index into an array of such types. The type associates
  * the file descriptor to the file state and to a set of inode operations.
@@ -497,7 +522,11 @@ struct file_struct
 {
   FAR struct file_struct *fs_next;      /* Pointer to next file stream */
   rmutex_t                fs_lock;      /* Recursive lock */
-  int                     fs_fd;        /* File descriptor associated with stream */
+  cookie_io_functions_t   fs_iofunc;    /* Callbacks to user / system functions */
+  FAR void               *fs_cookie;    /* Pointer to file descriptor / cookie struct */
+#ifdef CONFIG_FDSAN
+  uint8_t                 fs_hascookie;
+#endif
 #ifndef CONFIG_STDIO_DISABLE_BUFFERING
   FAR unsigned char      *fs_bufstart;  /* Pointer to start of buffer */
   FAR unsigned char      *fs_bufend;    /* Pointer to 1 past end of buffer */
@@ -1184,7 +1213,7 @@ int close_mtddriver(FAR struct inode *pinode);
  ****************************************************************************/
 
 #ifdef CONFIG_FILE_STREAM
-int fs_fdopen(int fd, int oflags, FAR struct tcb_s *tcb,
+int fs_fdopen(int fd, int cookie, int oflags, FAR struct tcb_s *tcb,
               FAR struct file_struct **filep);
 #endif
 

include/stdio.h

@@ -244,6 +244,11 @@ int    dprintf(int fd, FAR const IPTR char *fmt, ...) printf_like(2, 3);
 int    vdprintf(int fd, FAR const IPTR char *fmt, va_list ap)
        printf_like(2, 0);
 
+/* Custom stream operation fopencookie. */
+
+FAR FILE *fopencookie(FAR void *cookie, FAR const char *mode,
+                      cookie_io_functions_t io_funcs);
+
 /* Operations on paths */
 
 FAR FILE *tmpfile(void) fopen_like;

include/sys/syscall_lookup.h

@@ -274,7 +274,7 @@ SYSCALL_LOOKUP(munmap,                     2)
 #endif
 
 #ifdef CONFIG_FILE_STREAM
-  SYSCALL_LOOKUP(fs_fdopen,                4)
+  SYSCALL_LOOKUP(fs_fdopen,                5)
 #endif
 
 #ifndef CONFIG_DISABLE_MOUNTPOINT

libs/libc/libc.h

@@ -245,6 +245,13 @@ bool lib_isbasedigit(int ch, int base, FAR int *value);
 
 int lib_checkbase(int base, FAR const char **pptr);
 
+/* Defined in lib_stdio_cb.c */
+
+ssize_t lib_fread_cb(FAR void *cookie, FAR char *buf, size_t size);
+ssize_t lib_fwrite_cb(FAR void *cookie, FAR const char *buf, size_t size);
+off_t lib_fseek_cb(FAR void *cookie, FAR off_t *offset, int whence);
+int lib_fclose_cb(FAR void *cookie);
+
 /* Defined in lib_parsehostfile.c */
 
 #ifdef CONFIG_NETDB_HOSTFILE

libs/libc/stdio/CMakeLists.txt

@@ -104,7 +104,9 @@ if(CONFIG_FILE_STREAM)
     lib_libgetstreams.c
     lib_fputwc.c
     lib_putwc.c
-    lib_fputws.c)
+    lib_fputws.c
+    lib_fopencookie.c
+    lib_stdio_cb.c)
 endif()
 
 target_sources(c PRIVATE ${SRCS})

libs/libc/stdio/Make.defs

@@ -48,6 +48,7 @@ CSRCS += lib_feof.c lib_ferror.c lib_rewind.c lib_clearerr.c
 CSRCS += lib_scanf.c lib_vscanf.c lib_fscanf.c lib_vfscanf.c lib_tmpfile.c
 CSRCS += lib_setbuf.c lib_setvbuf.c lib_libstream.c lib_libfilelock.c
 CSRCS += lib_libgetstreams.c lib_setbuffer.c lib_fputwc.c lib_putwc.c lib_fputws.c
+CSRCS += lib_fopencookie.c lib_stdio_cb.c
 endif
 
 # Add the stdio directory to the build

libs/libc/stdio/lib_fclose.c

@@ -115,32 +115,41 @@ int fclose(FAR FILE *stream)
 
       nxmutex_unlock(&slist->sl_lock);
 
-      /* Check that the underlying file descriptor corresponds to an an open
-       * file.
-       */
+      /* Close the file descriptor and save the return status */
 
-      if (stream->fs_fd >= 0)
+#ifdef CONFIG_FDSAN
+      if (stream->fs_hascookie == 0)
         {
-          /* Close the file descriptor and save the return status */
+          /* This is a little warkaround. Ideally we would want to call
+           * fs_iofunc.close and let that handle it. FDSAN however requires
+           * stream to create owner tag and this is not avalialble in
+           * STDIO callback. This warkaround is used instead. It adds
+           * one if statement to fclose but overall is cheaper than
+           * passing entire stream to callback.
+           */
 
-#ifdef CONFIG_FDSAN
-          uint64_t tag;
-          tag = android_fdsan_create_owner_tag(ANDROID_FDSAN_OWNER_TYPE_FILE,
-                                               (uintptr_t)stream);
-          status = android_fdsan_close_with_tag(stream->fs_fd, tag);
+          int fd = (int)(intptr_t)stream->fs_cookie;
+          uint64_t tag = android_fdsan_create_owner_tag(
+                                        ANDROID_FDSAN_OWNER_TYPE_FILE,
+                                        (uintptr_t)stream);
+          return android_fdsan_close_with_tag(fd, tag);
+        }
+      else
+        {
+          status = stream->fs_iofunc.close(stream->fs_cookie);
+        }
 #else
-          status = close(stream->fs_fd);
+      status = stream->fs_iofunc.close(stream->fs_cookie);
 #endif
 
-          /* If close() returns an error but flush() did not then make sure
-           * that we return the close() error condition.
-           */
+      /* If close() returns an error but flush() did not then make sure
+       * that we return the close() error condition.
+       */
 
-          if (ret == OK)
-            {
-              ret = status;
-              errcode = get_errno();
-            }
+      if (ret == OK)
+        {
+          ret = status;
+          errcode = get_errno();
         }
 
 #ifndef CONFIG_STDIO_DISABLE_BUFFERING

libs/libc/stdio/lib_fileno.c

@@ -41,7 +41,7 @@ int fileno(FAR FILE *stream)
 
   if (stream)
     {
-      ret = stream->fs_fd;
+      ret = (int)(intptr_t)stream->fs_cookie;
     }
 
   if (ret < 0)

libs/libc/stdio/lib_fopen.c

@@ -74,7 +74,7 @@ FAR FILE *fdopen(int fd, FAR const char *mode)
   oflags = lib_mode2oflags(mode);
   if (oflags >= 0)
     {
-      ret = fs_fdopen(fd, oflags, NULL, &filep);
+      ret = fs_fdopen(fd, 0, oflags, NULL, &filep);
       if (ret < 0)
         {
           set_errno(-ret);
@@ -87,6 +87,13 @@ FAR FILE *fdopen(int fd, FAR const char *mode)
                                      (uintptr_t)filep));
 #endif
 
+  /* Assign internal callbacks. */
+
+  filep->fs_iofunc.read  = lib_fread_cb;
+  filep->fs_iofunc.write = lib_fwrite_cb;
+  filep->fs_iofunc.seek  = lib_fseek_cb;
+  filep->fs_iofunc.close = lib_fclose_cb;
+
   return filep;
 }
 
@@ -120,7 +127,7 @@ FAR FILE *fopen(FAR const char *path, FAR const char *mode)
 
   if (fd >= 0)
     {
-      ret = fs_fdopen(fd, oflags, NULL, &filep);
+      ret = fs_fdopen(fd, 0, oflags, NULL, &filep);
       if (ret < 0)
         {
           /* Don't forget to close the file descriptor if any other
@@ -140,6 +147,13 @@ FAR FILE *fopen(FAR const char *path, FAR const char *mode)
                                        (uintptr_t)filep));
 #endif
 
+  /* Assign internal callbacks. */
+
+  filep->fs_iofunc.read  = lib_fread_cb;
+  filep->fs_iofunc.write = lib_fwrite_cb;
+  filep->fs_iofunc.seek  = lib_fseek_cb;
+  filep->fs_iofunc.close = lib_fclose_cb;
+
   return filep;
 }
 

libs/libc/stdio/lib_fopencookie.c

@@ -0,0 +1,83 @@
+/****************************************************************************
+ * libs/libc/stdio/lib_fopencookie.c
+ *
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.  The
+ * ASF licenses this file to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance with the
+ * License.  You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+ * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.  See the
+ * License for the specific language governing permissions and limitations
+ * under the License.
+ *
+ ****************************************************************************/
+
+/****************************************************************************
+ * Included Files
+ ****************************************************************************/
+
+#include <nuttx/config.h>
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <unistd.h>
+#include <fcntl.h>
+#include <string.h>
+#include <assert.h>
+#include <errno.h>
+#include <nuttx/tls.h>
+
+#include "libc.h"
+
+/****************************************************************************
+ * Private Types
+ ****************************************************************************/
+
+/****************************************************************************
+ * Private Functions
+ ****************************************************************************/
+
+/****************************************************************************
+ * Public Functions
+ ****************************************************************************/
+
+/****************************************************************************
+ * Name: fopencookie
+ ****************************************************************************/
+
+FAR FILE *fopencookie(FAR void *cookie, FAR const char *mode,
+                      cookie_io_functions_t io_funcs)
+{
+  FAR FILE *filep = NULL;
+  int ret;
+  int oflags;
+
+  /* Map the open mode string to open flags */
+
+  oflags = lib_mode2oflags(mode);
+  if (oflags < 0)
+    {
+      return NULL;
+    }
+
+  /* Call fs_fdopen with invalid file descriptor and cookie flag set to 1 */
+
+  ret = fs_fdopen(-1, 1, oflags, NULL, &filep);
+  if (ret < 0)
+    {
+      return NULL;
+    }
+
+  /* Assign cookie and user defined callbacks. */
+
+  filep->fs_cookie = cookie;
+  filep->fs_iofunc = io_funcs;
+
+  return filep;
+}

libs/libc/stdio/lib_fseeko.c

@@ -87,5 +87,6 @@ int fseeko(FAR FILE *stream, off_t offset, int whence)
 
   /* Perform the fseeko on the underlying file descriptor */
 
-  return lseek(stream->fs_fd, offset, whence) == (off_t)-1 ? ERROR : OK;
+  return stream->fs_iofunc.seek(stream->fs_cookie, &offset,
+                                whence) == (off_t)-1 ? ERROR : OK;
 }

libs/libc/stdio/lib_ftello.c

@@ -97,6 +97,7 @@ static off_t lib_getoffset(FAR FILE *stream)
 off_t ftello(FAR FILE *stream)
 {
   off_t position;
+  off_t offset = 0;
 
   /* Verify that we were provided with a stream */
 
@@ -110,7 +111,7 @@ off_t ftello(FAR FILE *stream)
    * file pointer, but will return its current setting
    */
 
-  position = lseek(stream->fs_fd, 0, SEEK_CUR);
+  position = stream->fs_iofunc.seek(stream->fs_cookie, &offset, SEEK_CUR);
   if (position != (off_t)-1)
     {
       return position - lib_getoffset(stream);

libs/libc/stdio/lib_libfflush.c

@@ -65,7 +65,7 @@ ssize_t lib_fflush_unlocked(FAR FILE *stream, bool bforce)
 
   /* Return EBADF if the file is not opened for writing */
 
-  if (stream->fs_fd < 0 || (stream->fs_oflags & O_WROK) == 0)
+  if ((stream->fs_oflags & O_WROK) == 0)
     {
       return -EBADF;
     }
@@ -107,7 +107,9 @@ ssize_t lib_fflush_unlocked(FAR FILE *stream, bool bforce)
         {
           /* Perform the write */
 
-          bytes_written = _NX_WRITE(stream->fs_fd, src, nbuffer);
+          bytes_written = stream->fs_iofunc.write(stream->fs_cookie,
+                                                  (const char *)src,
+                                                   nbuffer);
           if (bytes_written < 0)
             {
               /* Write failed.  The cause of the failure is in 'errno'.