Donny9 opened a new issue, #6710:
URL: https://github.com/apache/incubator-nuttx/issues/6710
# Issue
The dup operation of nuttx is different from that of freebsd and opengroup.
* Nuttx
The old file descriptor and the new file descriptor generated by dup and
dup2 don't share the file entity and are independent of each other. They
correspond to different struct file entities in the filelist.
A file descriptor is an index into an fl_files array of sruct file. The
struct file associates the file descriptor to the file state and to a set of
inode operations.
```
struct file
{
int f_oflags; /* Open mode flags */
off_t f_pos; /* File position */
FAR struct inode *f_inode; /* Driver or file system interface */
FAR void *f_priv; /* Per file driver private data */
};
/* This defines a two layer array of files indexed by the file descriptor.
* Each row of this array is fixed size:
CONFIG_NFILE_DESCRIPTORS_PER_BLOCK.
* You can get file instance in filelist by the follow methods:
* (file descriptor / CONFIG_NFILE_DESCRIPTORS_PER_BLOCK) as row index and
* (file descriptor % CONFIG_NFILE_DESCRIPTORS_PER_BLOCK) as column index.
*/
struct filelist
{
sem_t fl_sem; /* Manage access to the file list */
uint8_t fl_rows; /* The number of rows of fl_files array */
FAR struct file **fl_files; /* The pointer of two layer file
descriptors array */
};
```
* FreeBSD/OpenGroup:
* Do you have good idea to fix this issue?
In view of the above problems, it will cause some problems in the
application of using dup, dup2 and fcntl on nuttx.
Here is one of the methods:
I will use filenode to correspond to file descriptor one-to-one, and
multiple filenodes can correspond to a unified file entity, When dup occurs,
the file pointer corresponding to the old filenode can be copied to the new
filenode to ensure sharing.
```
struct file
{
int16_t f_crefs; /* References to file */
int f_oflags; /* Open mode flags */
off_t f_pos; /* File position */
FAR struct inode *f_inode; /* Driver or file system interface */
FAR void *f_priv; /* Per file driver private data */
};
/* A file descriptor is an index into an array of such types. The type is
used to
* multiple file descriptor to share the same open file, include file offset
and
* file status flags, buf don't share file descriptor flags "close-on-exec
flag".
*/
struct filenode
{
int fn_oflags; /* Open or duplicate mode flags */
FAR struct file *fn_file; /* The pointer representation of an open
file */
};
/* This defines a two layer array of files indexed by the file descriptor.
* Each row of this array is fixed size: CONFIG_NFILE_DESCRIPTORS_PER_BLOCK.
* You can get file instance in filelist by the follow methods:
* (file descriptor / CONFIG_NFILE_DESCRIPTORS_PER_BLOCK) as row index and
* (file descriptor % CONFIG_NFILE_DESCRIPTORS_PER_BLOCK) as column index.
*/
struct filelist
{
sem_t fl_sem; /* Manage access to the file list */
uint8_t fl_rows; /* The number of rows of fl_files array */
FAR struct filenode **fl_files; /* The pointer of two layer file
descriptors array */
};
```
And it also needs to modify file_openation:dup, directly delete or remove
unnecessary features.
# Refer to
https://www.freebsd.org/cgi/man.cgi?query=dup&sektion=2
https://pubs.opengroup.org/onlinepubs/009604499/functions/dup.html
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