servers/procfs/type.h
#ifndef _PROCFS_TYPE_H
#define _PROCFS_TYPE_H

typedef void *data_t;		/* abstract data type; can hold pointer */

struct load {
	clock_t ticks;		/* in this umber of ticks: */
	long proc_load;		/* .. the CPU had this load */
};

/* ProcFS supports two groups of files: dynamic files, which are created within
 * process-specific (PID) directories, and static files, which are global. For
 * both, the following structure is used to construct the files.
 *
 * For dynamic files, the rules are simple: only regular files are supported
 * (although partial support for symbolic links is already present), and the
 * 'data' field must be filled with a pointer to a function of the type:
 *
 *   void (*)(int slot)
 *
 * The function will be called whenever a read request for the file is made;
 * 'slot' contains the kernel slot number of the process being queried (so for
 * the PM and VFS process tables, NR_TASKS has to be subtracted from the slot
 * number to find the right slot). The function is expected to produce
 * appropriate output using the buf_printf() function.
 *
 * For static files, regular files and directories are supported. For
 * directories, the 'data' field must be a pointer to another 'struct file'
 * array that specifies the contents of the directory - this directory will
 * the be created recursively. For regular files, the 'data' field must point
 * to a function of the type:
 *
 *   void (*)(void)
 *
 * Here too, the function will be called upon a read request, and it is
 * supposed to "fill" the file using buf_printf(). Obviously, for static files,
 * there is no slot number.
 *
 * For both static and dynamic files, 'mode' must specify the file type as well
 * as the access mode, and in both cases, each array is terminated with an
 * entry that has its name set to NULL.
 */
/* The internal link between static/dynamic files/directories and VTreeFS'
 * indexes and cbdata values is as follows:
 * - Dynamic directories are always PID directories in the root directory.
 *   They are generated automatically, and are not specified using a "struct
 *   file" structure. Their index is their slot number, so that getdents()
 *   calls always return any PID at most once. Their cbdata value is the PID of
 *   the process associated with that dynamic directory, for the purpose of
 *   comparing old and new PIDs after updating process tables (without having
 *   to atoi() the directory's name).
 * - Dynamic files are always in such a dynamic directory. Their index is the
 *   array index into the "struct file" array of pid files (pid_files[]). They
 *   are indexed at all, because they may be deleted at any time due to inode
 *   shortages, independently of other dynamic files in the same directory, and
 *   recreating them without index would again risk possibly inconsistent
 *   getdents() results, where for example the same file shows up twice.
 *   VTreeFS currently does not distinguish between indexed and delatable files
 *   and hence, all dynamic files must be indexed so as to be deletable anyway.
 * - Static directories have no index (they are not and must not be deletable),
 *   and although their cbdata is their associated 'data' field from their
 *   "struct file" entries, their cbdata value is currently not relied on
 *   anywhere. Then again, as of writing, there are no static directories at
 *   all.
 * - Static files have no index either (for the same reason). Their cbdata is
 *   also their 'data' field from the "struct file" entry creating the file,
 *   and this is used to actually call the callback function directly.
 */
struct file {
	char *name;		/* file name, maximum length PNAME_MAX */
	mode_t mode;		/* file mode, including file type */
	data_t data;		/* custom data associated with this file */
};

#endif /* _PROCFS_TYPE_H */
