matos/core/fsEntry.h

#pragma once

#include "fs.h"
#include "stdint.h"
#include "stddef.h"

/**
 * Those structures aimes to represent VFS directory entries in memory.
 * It's the equivalent of the Linux dentry or SimpleOs sos_fs_nscache_node.
 */

/**
 * Path or Pascal String
 * */
struct pstr {
    size_t len;
    const char *name;
};

#define PSTR_INIT(n, l)                                                                       \
    {                                                                                         \
        .len = l, .name = n                                                                   \
    }

#define PSTR_STATIC_INIT(n)                                                                   \
    {                                                                                         \
        .len = sizeof(n) - 1, .name = n                                                       \
    }

/**
 * @brief Structure representing a file system entry.
 *
 * This structure holds information about a file system entry,
 * including its name, associated inode, relationships within
 * the file system hierarchy, and reference count.
 */
struct fs_entry {
    struct pstr name;
    struct inode *node;

    struct fs_entry *parent;     // parent directory
    struct fs_entry *mountpoint; // if this is a mounted fs, point to mountpoint
    struct fs_entry *mountedFs;  // Fs possibly mounted on this fsEntry

    struct fs_entry *childs;                      // point to the list of children
    struct fs_entry *nextSiblings, *prevSiblings; // Sibling at the same level

    uint ref; // reference counter
};

/**
 * @brief Splits a pstr path into upper and lower components.
 *
 * This function takes a path and splits it into an upper component
 * (the first segment of the path) and a lower component (the rest of the path).
 *
 * @param path Pointer to the input pstr structure representing the path.
 * @param upper Pointer to the pstr structure to store the upper component.
 * @param lower Pointer to the pstr structure to store the lower component.
 * @return bool_t Returns true if there is a lower component, false otherwise.
 */
bool_t pstringSplipPath(struct pstr *path, struct pstr *upper, struct pstr *lower);

/**
 * @brief Compares two pstr structures to check if they are equal.
 *
 * This function compares the length and the content of the strings
 * in the two provided pstr structures.
 *
 * @param a Pointer to the first pstr structure.
 * @param b Pointer to the second pstr structure.
 * @return int Returns 1 if the structures are equal, 0 otherwise.
 */
bool_t pstringIsEq(const struct pstr *p1, const struct pstr *p2);

/**
 * @brief Checks if a pstr structure matches a given C string.
 *
 * @param s Pointer to the null-terminated C string to compare.
 * @return bool_t Returns true if the pstr matches the C string, false otherwise.
 */
bool_t pstringIsStr(const struct pstr *p, char *s);

/**
 * @brief Increments the reference count of a file system entry.
 *
 * This function increments the reference count of the given file system
 * entry. It is typically used to manage the lifecycle of file system
 * entries, ensuring that they are not prematurely deallocated.
 *
 * @param entry Pointer to the fsEntry structure whose reference count will be incremented.
 * @return int Returns 0 on success.
 */
int fsEntryRef(struct fs_entry *entry);

/**
 * @brief Decrements the reference count of a file system entry.
 *
 * This function decrements the reference count of the given file system
 * entry. It is typically used to manage the lifecycle of file system
 * entries, ensuring that they are not prematurely deallocated.
 *
 * @param entry Pointer to the fsEntry structure whose reference count will be decremented.
 * @return int Returns 0 on success.
 */
int fsEntryUnref(struct fs_entry **entry);

/**
 * @brief Allocates and initializes a new fsEntry.
 *
 * This function allocates memory for a new `fsEntry` structure, initializes
 * it with the provided name and inode, and adds it to the parent's list of children.
 *
 * @param parent Pointer to the parent `fsEntry` structure. Can be NULL if the new entry has no parent.
 * @param name Pointer to the `pstr` structure representing the name of the new entry. Can be NULL.
 * @param inode Pointer to the `inode` structure associated with the new entry.
 *
 * @return struct fsEntry* Pointer to the newly allocated `fsEntry` structure, or NULL if allocation fails.
 *
 * @note The reference count of the new entry is set to 1.
 * @note If a parent is provided, the new entry is added to the parent's list of children and the parent's reference count is incremented.
 * @note The inode's reference count is incremented.
 */
struct fs_entry *fsEntryAlloc(struct fs_entry *parent, const struct pstr *name, struct inode *inode);

/**
 * @brief Looks up an entry in the file system.
 *
 * This function searches for a specified entry within the children
 * of a given directory entry. The search is limited to the entries
 * that are already in memory. If the entry is not found, it indicates
 * that the entry must be resolved using disk accesses.
 *
 * @param entry The node in which we are looking for the entry.
 * @param name The name of the entry we are looking for.
 * @param root The base node beyond which lookup must not go (to
 * support chroot): a kind of "barrier".
 * @param result The fsEntry for the given entry (set only when
 * the return value is 0).
 *
 * @return int Returns 0 if the entry is found, otherwise returns a non-zero error code.
 *         -ENOENT if the entry could not be found in the entry directory.
 *
 * @note The mountpoints are followed.
 * @note result is a NEW reference to the node. It should be unreferenced when unused.
 */
int fsEntryLookup(struct fs_entry *entry, const struct pstr *name,
                          const struct fs_entry *root, struct fs_entry **result);
/**
 * @brief Setup the fsEntry subsystem
 *
 */
int fsEntrySetup(void);

/**
 * @brief Mounts a file system entry at a specified mount point.
 *
 * This function mounts a file system entry (`mounted`) at a specified mount point (`mountpoint`).
 * It updates the `mountedFs` field of the mount point and the `mountpoint` field of the mounted entry.
 *
 * @param mountpoint Pointer to the `fsEntry` structure representing the mount point.
 * @param mounted Pointer to the `fsEntry` structure representing the file system entry to be mounted.
 *
 * @return int Returns 0 on success, or -EBUSY if either the mount point is already occupied or the mounted entry is already mounted.
 *
 * @note The reference counts of both the mount point and the mounted entry are incremented.
 */
int fsEntryMount(struct fs_entry *mountpoint, struct fs_entry *mounted);

/**
 * @brief Unmounts a file system entry.
 *
 * This function unmounts a file system entry (`mounted`) from its mount point.
 * It updates the `mountedFs` field of the mount point and the `mountpoint` field of the mounted entry.
 *
 * @param mounted Pointer to the `fsEntry` structure representing the file system entry to be unmounted.
 *
 * @return int Returns 0 on success, -ENOENT if the entry is not mounted, or -EBUSY if the entry is busy.
 *
 * @note The unmount operation fails if the mounted entry has children or other references.
 * @note The reference counts of both the mount point and the mounted entry are decremented.
 */
int fsEntryUmount(struct fs_entry *mounted);