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).

The interface will be useful for future fmemopen implementation.

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

include/nuttx/fs/fs.h

@@ -425,6 +425,55 @@ 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.
+ */
+
+typedef ssize_t cookie_read_function_t(void *cookie, char *buf, size_t size);
+typedef ssize_t cookie_write_function_t(void *cookie, const char *buf,
+                                        size_t size);
+typedef off_t cookie_seek_function_t(void *cookie, off_t *offset,
+                                     int whence);
+typedef int cookie_close_function_t(void *cookie);
+
+typedef struct
+{
+  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;
+
+struct cookie_s
+{
+  FAR void *cookie;                /* Pointer to the caller's cookie struct */
+  cookie_io_functions_t cookie_io; /* Programmer-defined hook functions */
+};
+
+/* Definition of internal callbacks for read/write/seek/close operations.
+ * These are needed to ensure custom callbacks from fopencookie are called
+ * from user address space and not from kernel address space. These callbacks
+ * are either routed to fopencookie related callbacks or to internal
+ * read/write/seek/close operations defined in file system (thus in kernel
+ * address space)
+ */
+
+typedef ssize_t read_internal_cb_t(FAR void *s, char *buf, size_t size);
+typedef ssize_t write_internal_cb_t(FAR void *s, const char *buf,
+                                    size_t size);
+typedef off_t seek_internal_cb_t(FAR void *s, off_t offset, int whence);
+typedef int close_internal_cb_t(FAR void *s);
+
+typedef struct
+{
+  FAR read_internal_cb_t *read;
+  FAR write_internal_cb_t *write;
+  FAR seek_internal_cb_t *seek;
+  FAR close_internal_cb_t *close;
+} io_callbacks_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.
@@ -497,6 +546,8 @@ 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 */
+  FAR struct cookie_s     fs_cookie;    /* Cookie structure for fopencookie */
+  io_callbacks_t          fs_callbacks; /* Internal callbacks for IO call */
 #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 */

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;

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 */
+
+ssize_t lib_fread_cb(void *stream, char *buf, size_t size);
+ssize_t lib_fwrite_cb(void *stream, const char *buf, size_t size);
+off_t lib_fseek_cb(void *stream, off_t offset, int whence);
+int lib_fclose_cb(void *stream);
+
 /* Defined in lib_parsehostfile.c */
 
 #ifdef CONFIG_NETDB_HOSTFILE

libs/libc/stdio/CMakeLists.txt

@@ -100,7 +100,9 @@ if(CONFIG_FILE_STREAM)
     lib_setvbuf.c
     lib_libstream.c
     lib_libfilelock.c
-    lib_libgetstreams.c)
+    lib_libgetstreams.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
+CSRCS += lib_fopencookie.c lib_stdio_cb.c
 endif
 
 # Add the stdio directory to the build

libs/libc/stdio/lib_fclose.c

@@ -129,7 +129,7 @@ int fclose(FAR FILE *stream)
                                                (uintptr_t)stream);
           status = android_fdsan_close_with_tag(stream->fs_fd, tag);
 #else
-          status = close(stream->fs_fd);
+          status = stream->fs_callbacks.close(stream);
 #endif
 
           /* If close() returns an error but flush() did not then make sure

libs/libc/stdio/lib_fopen.c

@@ -87,6 +87,11 @@ FAR FILE *fdopen(int fd, FAR const char *mode)
                                      (uintptr_t)filep));
 #endif
 
+  filep->fs_callbacks.read  = lib_fread_cb;
+  filep->fs_callbacks.write = lib_fwrite_cb;
+  filep->fs_callbacks.seek  = lib_fseek_cb;
+  filep->fs_callbacks.close = lib_fclose_cb;
+
   return filep;
 }
 
@@ -140,6 +145,11 @@ FAR FILE *fopen(FAR const char *path, FAR const char *mode)
                                        (uintptr_t)filep));
 #endif
 
+  filep->fs_callbacks.read  = lib_fread_cb;
+  filep->fs_callbacks.write = lib_fwrite_cb;
+  filep->fs_callbacks.seek  = lib_fseek_cb;
+  filep->fs_callbacks.close = lib_fclose_cb;
+
   return filep;
 }
 

libs/libc/stdio/lib_fopencookie.c

@@ -0,0 +1,181 @@
+/****************************************************************************
+ * 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
+ ****************************************************************************/
+
+static ssize_t freadcookie(FAR void *s, FAR char *buf, size_t nbytes);
+static ssize_t fwritecookie(FAR void *s, FAR const char *buf, size_t nbytes);
+static off_t fseekcookie(FAR void *s, off_t offset, int whence);
+static int fclosecookie(FAR void *s);
+
+/****************************************************************************
+ * Private Functions
+ ****************************************************************************/
+
+static FAR FILE *fopencookie_init_stream(int oflags)
+{
+  FAR FILE *stream;
+
+  stream = lib_zalloc(sizeof(FILE));
+  if (stream == NULL)
+    {
+      set_errno(-ENOMEM);
+      return NULL;
+    }
+
+  nxrmutex_init(&stream->fs_lock);
+
+#ifndef CONFIG_STDIO_DISABLE_BUFFERING
+#if CONFIG_STDIO_BUFFER_SIZE > 0
+  /* Set up pointers */
+
+  stream->fs_bufstart = stream->fs_buffer;
+  stream->fs_bufend   = &stream->fs_bufstart[CONFIG_STDIO_BUFFER_SIZE];
+  stream->fs_bufpos   = stream->fs_bufstart;
+  stream->fs_bufread  = stream->fs_bufstart;
+  stream->fs_flags    = __FS_FLAG_UBF; /* Fake setvbuf and fclose */
+
+#ifdef CONFIG_STDIO_LINEBUFFER
+  /* Setup buffer flags */
+
+  stream->fs_flags   |= __FS_FLAG_LBF; /* Line buffering */
+
+#endif /* CONFIG_STDIO_LINEBUFFER */
+#endif /* CONFIG_STDIO_BUFFER_SIZE > 0 */
+#endif /* CONFIG_STDIO_DISABLE_BUFFERING */
+
+  /* Save the file description and open flags.  Setting the
+   * file descriptor locks this stream.
+   */
+
+  stream->fs_fd       = -1;
+  stream->fs_oflags   = oflags;
+
+  return stream;
+}
+
+static ssize_t freadcookie(FAR void *s, FAR char *buf, size_t nbytes)
+{
+  FAR FILE *stream = (FAR FILE *)s;
+  FAR struct cookie_s *cookie = (FAR struct cookie_s *)&stream->fs_cookie;
+  int ret;
+
+  DEBUGASSERT(cookie->cookie != NULL && cookie->cookie_io.read != NULL);
+
+  ret = cookie->cookie_io.read(cookie->cookie, buf, nbytes);
+  return ret;
+}
+
+static ssize_t fwritecookie(FAR void *s, FAR const char *buf, size_t nbytes)
+{
+  FAR FILE *stream = (FAR FILE *)s;
+  FAR struct cookie_s *cookie = (FAR struct cookie_s *)&stream->fs_cookie;
+  int ret;
+
+  DEBUGASSERT(cookie->cookie != NULL && cookie->cookie_io.write != NULL);
+
+  ret = cookie->cookie_io.write(cookie->cookie, buf, nbytes);
+  return ret;
+}
+
+static off_t fseekcookie(FAR void *s, off_t offset, int whence)
+{
+  FAR FILE *stream = (FAR FILE *)s;
+  FAR struct cookie_s *cookie = (FAR struct cookie_s *)&stream->fs_cookie;
+  int ret;
+
+  DEBUGASSERT(cookie->cookie != NULL && cookie->cookie_io.seek != NULL);
+
+  ret = cookie->cookie_io.seek(cookie->cookie, &offset, whence);
+  return ret;
+}
+
+static int fclosecookie(FAR void *s)
+{
+  FAR FILE *stream = (FAR FILE *)s;
+  FAR struct cookie_s *cookie = (FAR struct cookie_s *)&stream->fs_cookie;
+  int ret;
+
+  DEBUGASSERT(cookie->cookie != NULL && cookie->cookie_io.close != NULL);
+
+  ret = cookie->cookie_io.close(cookie->cookie);
+
+  free(stream);
+
+  return ret;
+}
+
+/****************************************************************************
+ * 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 oflags;
+
+  /* Map the open mode string to open flags */
+
+  oflags = lib_mode2oflags(mode);
+  if (oflags < 0)
+    {
+      return NULL;
+    }
+
+  filep = fopencookie_init_stream(oflags);
+  if (filep == NULL)
+    {
+      return NULL;
+    }
+
+  filep->fs_cookie.cookie    = cookie;
+  filep->fs_cookie.cookie_io = io_funcs;
+
+  filep->fs_callbacks.read  = freadcookie;
+  filep->fs_callbacks.write = fwritecookie;
+  filep->fs_callbacks.seek  = fseekcookie;
+  filep->fs_callbacks.close = fclosecookie;
+
+  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_callbacks.seek(stream, offset, whence) == (off_t)-1 ?
+         ERROR : OK;
 }

libs/libc/stdio/lib_ftello.c

@@ -110,7 +110,7 @@ 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_callbacks.seek(stream, 0, 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_callbacks.write(stream,
+                                                     (const char *)src,
+                                                     nbuffer);
           if (bytes_written < 0)
             {
               /* Write failed.  The cause of the failure is in 'errno'.

libs/libc/stdio/lib_libfread_unlocked.c

@@ -170,7 +170,9 @@ ssize_t lib_fread_unlocked(FAR void *ptr, size_t count, FAR FILE *stream)
 
                   if (remaining > buffer_available)
                     {
-                      bytes_read = _NX_READ(stream->fs_fd, dest, remaining);
+                      bytes_read = stream->fs_callbacks.read(stream,
+                                                             (char *)dest,
+                                                             remaining);
                       if (bytes_read < 0)
                         {
                           if (count - remaining > 0)
@@ -213,9 +215,9 @@ ssize_t lib_fread_unlocked(FAR void *ptr, size_t count, FAR FILE *stream)
                        * into the buffer.
                        */
 
-                      bytes_read = _NX_READ(stream->fs_fd,
-                                            stream->fs_bufread,
-                                            buffer_available);
+                      bytes_read = stream->fs_callbacks.read(stream,
+                                              (char *)stream->fs_bufread,
+                                              buffer_available);
                       if (bytes_read < 0)
                         {
                           if (count - remaining > 0)
@@ -258,7 +260,8 @@ ssize_t lib_fread_unlocked(FAR void *ptr, size_t count, FAR FILE *stream)
 
           while (remaining > 0)
             {
-              bytes_read = _NX_READ(stream->fs_fd, dest, remaining);
+              bytes_read = stream->fs_callbacks.read(stream, (char *)dest,
+                                                     remaining);
               if (bytes_read < 0)
                 {
                   if (count - remaining > 0)