Add VFS subsystem and initrd filesystem driver (AI)
VFS subsystem (vfs.c/h): - Mount table with up to 16 mount points, longest-prefix path matching. - File descriptor table (256 entries, fds 0-2 reserved for std streams). - Path resolution walks mount table then delegates to filesystem's finddir() for each path component. - Operations: open, close, read, write, seek, readdir, stat. - Each filesystem driver provides a vfs_fs_ops_t with callbacks. Initrd filesystem driver (initrd_fs.c/h): - Read-only VFS driver backed by the CPIO ramdisk. - Mounted at '/initrd' during boot. - Zero-copy reads: file data points directly into the CPIO archive memory, no allocation or copying needed. - Supports readdir (flat iteration) and finddir (name lookup). Bug fix: resolve_path was overwriting file-specific fs_data (set by finddir, e.g. pointer to CPIO file data) with the mount's fs_data (NULL). Fixed to preserve fs_data from finddir. Verified in QEMU: kernel reads /initrd/README via VFS and prints its contents. Ring 3 user process continues to work.
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AI
197
src/vfs.h
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197
src/vfs.h
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/**
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* @file vfs.h
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* @brief Virtual Filesystem (VFS) subsystem.
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*
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* Provides a unified interface for file and directory operations across
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* different filesystem implementations. Filesystem drivers register
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* themselves and can be mounted at specific paths.
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*/
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#ifndef VFS_H
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#define VFS_H
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#include <stdint.h>
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#include <stddef.h>
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/** Maximum number of open files across all processes. */
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#define VFS_MAX_OPEN_FILES 256
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/** Maximum number of mounted filesystems. */
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#define VFS_MAX_MOUNTS 16
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/** Maximum path length. */
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#define VFS_MAX_PATH 256
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/** Maximum filename length. */
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#define VFS_MAX_NAME 128
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/** File types. */
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#define VFS_FILE 0x01
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#define VFS_DIRECTORY 0x02
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#define VFS_CHARDEV 0x03
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#define VFS_BLOCKDEV 0x04
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#define VFS_SYMLINK 0x06
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/** Seek origins. */
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#define VFS_SEEK_SET 0
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#define VFS_SEEK_CUR 1
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#define VFS_SEEK_END 2
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/** Forward declarations. */
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struct vfs_node;
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struct vfs_dirent;
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struct vfs_fs_ops;
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/**
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* Directory entry, returned by readdir.
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*/
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typedef struct vfs_dirent {
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char name[VFS_MAX_NAME]; /**< Entry name. */
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uint32_t inode; /**< Inode number (fs-specific). */
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uint8_t type; /**< VFS_FILE, VFS_DIRECTORY, etc. */
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} vfs_dirent_t;
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/**
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* VFS node representing a file or directory.
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*/
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typedef struct vfs_node {
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char name[VFS_MAX_NAME]; /**< Node name. */
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uint8_t type; /**< VFS_FILE, VFS_DIRECTORY, etc. */
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uint32_t size; /**< File size in bytes. */
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uint32_t inode; /**< Inode number (fs-specific). */
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uint32_t mode; /**< Permissions/mode. */
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/** Filesystem-specific operations. */
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struct vfs_fs_ops *ops;
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/** Opaque pointer for the filesystem driver. */
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void *fs_data;
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/** Mount index (which mount this node belongs to). */
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int mount_idx;
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} vfs_node_t;
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/**
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* Filesystem operations provided by each filesystem driver.
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*/
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typedef struct vfs_fs_ops {
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/** Open a file. Returns 0 on success. */
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int (*open)(vfs_node_t *node, uint32_t flags);
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/** Close a file. */
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void (*close)(vfs_node_t *node);
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/** Read up to `size` bytes at `offset`. Returns bytes read, or -1. */
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int32_t (*read)(vfs_node_t *node, uint32_t offset, uint32_t size, void *buf);
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/** Write up to `size` bytes at `offset`. Returns bytes written, or -1. */
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int32_t (*write)(vfs_node_t *node, uint32_t offset, uint32_t size, const void *buf);
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/** Read directory entry at index `idx`. Returns 0 on success, -1 at end. */
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int (*readdir)(vfs_node_t *dir, uint32_t idx, vfs_dirent_t *out);
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/** Look up a child by name within a directory. Returns 0 on success. */
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int (*finddir)(vfs_node_t *dir, const char *name, vfs_node_t *out);
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} vfs_fs_ops_t;
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/**
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* Mount point entry.
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*/
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typedef struct vfs_mount {
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char path[VFS_MAX_PATH]; /**< Mount path (e.g., "/initrd"). */
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vfs_fs_ops_t *ops; /**< Filesystem operations. */
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void *fs_data; /**< Filesystem-specific data. */
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int active; /**< 1 if mounted, 0 if free. */
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} vfs_mount_t;
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/**
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* Open file descriptor.
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*/
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typedef struct vfs_fd {
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vfs_node_t node; /**< The file node. */
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uint32_t offset; /**< Current read/write offset. */
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uint32_t flags; /**< Open flags. */
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int active; /**< 1 if in use, 0 if free. */
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} vfs_fd_t;
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/**
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* Initialize the VFS subsystem.
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*/
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void init_vfs(void);
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/**
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* Mount a filesystem at the given path.
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*
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* @param path Mount point path (e.g., "/initrd").
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* @param ops Filesystem operations.
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* @param fs_data Filesystem-specific data pointer.
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* @return 0 on success, -1 on failure.
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*/
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int vfs_mount(const char *path, vfs_fs_ops_t *ops, void *fs_data);
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/**
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* Open a file by path.
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*
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* @param path Absolute path to the file.
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* @param flags Open flags (currently unused).
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* @return File descriptor (>= 0), or -1 on failure.
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*/
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int vfs_open(const char *path, uint32_t flags);
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/**
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* Close an open file descriptor.
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*
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* @param fd File descriptor.
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*/
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void vfs_close(int fd);
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/**
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* Read from an open file.
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*
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* @param fd File descriptor.
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* @param buf Buffer to read into.
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* @param size Maximum bytes to read.
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* @return Bytes read, or -1 on error.
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*/
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int32_t vfs_read(int fd, void *buf, uint32_t size);
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/**
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* Write to an open file.
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*
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* @param fd File descriptor.
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* @param buf Buffer to write from.
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* @param size Bytes to write.
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* @return Bytes written, or -1 on error.
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*/
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int32_t vfs_write(int fd, const void *buf, uint32_t size);
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/**
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* Seek within an open file.
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*
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* @param fd File descriptor.
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* @param offset Offset to seek to.
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* @param whence VFS_SEEK_SET, VFS_SEEK_CUR, or VFS_SEEK_END.
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* @return New offset, or -1 on error.
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*/
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int32_t vfs_seek(int fd, int32_t offset, int whence);
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/**
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* Read a directory entry.
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*
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* @param path Path to the directory.
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* @param idx Entry index (0-based).
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* @param out Output directory entry.
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* @return 0 on success, -1 at end or on error.
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*/
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int vfs_readdir(const char *path, uint32_t idx, vfs_dirent_t *out);
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/**
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* Stat a file (get its node info).
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*
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* @param path Path to the file.
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* @param out Output node.
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* @return 0 on success, -1 on failure.
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*/
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int vfs_stat(const char *path, vfs_node_t *out);
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#endif /* VFS_H */
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