linuxkpi: Add `show_fdinfo()` to `struct file_operations`

[dumbbell]

Summary

We never call this field but it allows to compile drivers without modifications.

This is used by the DRM drivers for some time, but another change part of the update to Linux 6.8 led to compile them with CONFIG_PROC_FS. This connected code that uses this struct field.

This is part of the update of DRM drivers to Linux 6.8.

Sponsored by: The FreeBSD Foundation

[bz]

sys/compat/linuxkpi/common/include/linux/fs.h

157

No need for variable names in declarations (remove m and f) also to stay consistent with the rest of the file.

This likely warrants another __FreeBSD_version bump (so maybe do that when all changes are going in together).

[dumbbell]

Address style-related comment from bz

sys/compat/linuxkpi/common/include/linux/fs.h

struct file_operations {
         int (*release)(struct inode *, struct linux_file *);
         int (*fasync)(int, struct linux_file *, int);
 
 /* Although not supported in FreeBSD, to align with Linux code
  * we are adding llseek() only when it is mapped to no_llseek which returns
  * an illegal seek error
  */
         off_t (*llseek)(struct linux_file *, off_t, int);
+/*
+ * Not supported in FreeBSD. That's ok, we never call it and it allows some
+ * drivers like DRM drivers to compile without changes.
+ */
+        void (*show_fdinfo)(struct seq_file *, struct file *);
 #if 0
         /* We do not support these methods.  Don't permit them to compile. */
         loff_t (*llseek)(struct file *, loff_t, int);
         ssize_t (*aio_read)(struct kiocb *, const struct iovec *,
             unsigned long, loff_t);
         ssize_t (*aio_write)(struct kiocb *, const struct iovec *,
             unsigned long, loff_t);
         int (*readdir)(struct file *, void *, filldir_t);