xiaoxiang781216 commented on PR #10602:
URL: https://github.com/apache/nuttx/pull/10602#issuecomment-1719917277
> I once had a look at that to handle a `fomempen` and alike properly, it
would require that LIBC `struct FILE` not to be a direct alias to internal FS
struct, as indeed you need to keep a reference to fs operation callbacks and
permission flags, so it would require an indirection where `struct FILE` holds
a private pointer to internal. Meanwhile, I think LIBC stdio would benefit at
term that indirection to be made.
>
> ```c
> struct libc_stdio_file
> {
> // ... stdio specifics;
> libc_stdio_fread_t read;
> libc_stdio_fwrite_t write;
> libc_stdio_fseek_t seek;
> libc_stdio_fclose_t close;
> libc_stdio_cookie_t cookie;
>
> file_struct * internal;
> }
>
> typedef libc_stdio_file FILE;
> ```
we don't need add a new struct libc_stdio_file. Here is the current
definition:
```
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 */
#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 */
FAR unsigned char *fs_bufpos; /* Current position in buffer */
FAR unsigned char *fs_bufread; /* Pointer to 1 past last buffered
read char. */
# if CONFIG_STDIO_BUFFER_SIZE > 0
unsigned char fs_buffer[CONFIG_STDIO_BUFFER_SIZE];
# endif
#endif
uint16_t fs_oflags; /* Open mode flags */
uint8_t fs_flags; /* Stream flags */
#if CONFIG_NUNGET_CHARS > 0
uint8_t fs_nungotten; /* The number of characters buffered
for ungetc */
unsigned char fs_ungotten[CONFIG_NUNGET_CHARS];
#endif
};
typedef struct file_struct FILE;
```
Here is the simple change to the struct:
```
struct file_struct
{
...
- int fs_fd; /* File descriptor associated with
stream */
+ cookie_io_functions_t fs_iofunc;
+ FAR void * fs_cookie;
```
};
```
and replace all read/write/seek/close with
stream->iofunc.read/write/seek/close.
The remaining work is adding the simple wrapper for fopen:
```
static ssize_t read_fd(void *cookie, char *buf, size_t size)
{
int fd = (int)(intptr_t)cookie;
return read(fd, buf, size);
}
static ssize_t write(void *cookie, const char *buf, size_t size)
{
int fd = (int)(intptr_t)cookie;
return write(fd, buf, size);
}
static int seek(void *cookie, off_t *offset, int whence)
{
int fd = (int)(intptr_t)cookie;
off_t ret = seek(fd, *offset, whence);
if (ret >= 0)
{
*offset = ret;
ret = 0;
}
return ret;
}
```
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