In-Memory Filesystem

Contents

7. In-Memory Filesystem#

This chapter describes the In-Memory FileSystem (IMFS). The IMFS is a full featured POSIX filesystem that keeps all information in memory.

7.1. IMFS Per Node Data Structure#

Each regular file, device, hard link, and directory is represented by a data structure called a jnode. The jnode is formally represented by the structure:

struct IMFS_jnode_tt {
    Chain_Node          Node;             /* for chaining them together */
    IMFS_jnode_t       *Parent;           /* Parent node */
    char                name[NAME_MAX+1]; /* "basename" */
    mode_t              st_mode;          /* File mode */
    nlink_t             st_nlink;         /* Link count */
    ino_t               st_ino;           /* inode */
    uid_t               st_uid;           /* User ID of owner */
    gid_t               st_gid;           /* Group ID of owner */
    time_t              st_atime;         /* Time of last access */
    time_t              st_mtime;         /* Time of last modification */
    time_t              st_ctime;         /* Time of last status change */
    IMFS_jnode_types_t  type;             /* Type of this entry */
    IMFS_typs_union     info;
};

The key elements of this structure are listed below together with a brief explanation of their role in the filesystem.

Node

exists to allow the entire jnode structure to be included in a chain.

Parent

is a pointer to another jnode structure that is the logical parent of the node in which it appears. This field may be NULL if the file associated with this node is deleted but there are open file descriptors on this file or there are still hard links to this node.

name

is the name of this node within the filesystem hierarchical tree. Example: If the fully qualified pathname to the jnode was /a/b/c, the jnode name field would contain the null terminated string "c".

st_mode

is the standard Unix access permissions for the file or directory.

st_nlink

is the number of hard links to this file. When a jnode is first created its link count is set to 1. A jnode and its associated resources cannot be deleted unless its link count is less than 1.

st_ino

is a unique node identification number

st_uid

is the user ID of the file’s owner

st_gid

is the group ID of the file’s owner

st_atime

is the time of the last access to this file

st_mtime

is the time of the last modification of this file

st_ctime

is the time of the last status change to the file

type
is the indication of node type must be one of the following states:

  • IMFS_DIRECTORY

  • IMFS_MEMORY_FILE

  • IMFS_HARD_LINK

  • IMFS_SYM_LINK

  • IMFS_DEVICE

info

is this contains a structure that is unique to file type (See IMFS_typs_union in imfs.h).

  • IMFS_DIRECTORY

    An IMFS directory contains a dynamic chain structure that records all files and directories that are subordinate to the directory node.

  • IMFS_MEMORY_FILE

    Under the in memory filesystem regular files hold data. Data is dynamically allocated to the file in 128 byte chunks of memory. The individual chunks of memory are tracked by arrays of pointers that record the address of the allocated chunk of memory. Single, double, and triple indirection pointers are used to record the locations of all segments of the file. The memory organization of an IMFS file are discussed elsewhere in this manual.

  • IMFS_HARD_LINK

    The IMFS filesystem supports the concept of hard links to other nodes in the IMFS filesystem. These hard links are actual pointers to other nodes in the same filesystem. This type of link cannot cross-filesystem boundaries.

  • IMFS_SYM_LINK

    The IMFS filesystem supports the concept of symbolic links to other nodes in any filesystem. A symbolic link consists of a pointer to a character string that represents the pathname to the target node. This type of link can cross-filesystem boundaries. Just as with most versions of UNIX supporting symbolic links, a symbolic link can point to a non-existent file.

  • IMFS_DEVICE

    All RTEMS devices now appear as files under the in memory filesystem. On system initialization, all devices are registered as nodes under the file system.

7.2. Miscellaneous IMFS Information#

TBD

7.3. Memory associated with the IMFS#

A memory based filesystem draws its resources for files and directories from the memory resources of the system. When it is time to un-mount the filesystem, the memory resources that supported filesystem are set free. In order to free these resources, a recursive walk of the filesystems tree structure will be performed. As the leaf nodes under the filesystem are encountered their resources are freed. When directories are made empty by this process, their resources are freed.

7.3.1. Node removal constraints for the IMFS#

The IMFS conforms to the general filesystem requirements for node removal. See File and Directory Removal Constraints.

7.3.2. IMFS General Housekeeping Notes#

The following is a list of odd housekeeping notes for the IMFS.

  • If the global variable rtems_filesystem_current refers to the node that we are trying to remove, the node_access element of this structure must be set to NULL to invalidate it.

  • If the node was of IMFS_MEMORY_FILE type, free the memory associated with the memory file before freeing the node. Use the IMFS_memfile_remove() function.

7.4. IMFS Operation Tables#

7.4.1. IMFS Filesystem Handler Table Functions#

OPS table functions are defined in a rtems_filesystem_operations_table structure. It defines functions that are specific to a given filesystem. One table exists for each filesystem that is supported in the RTEMS configuration. The structure definition appears below and is followed by general developmental information on each of the functions contained in this function management structure.

rtems_filesystem_operations_table  IMFS_ops = {
    IMFS_eval_path,
    IMFS_evaluate_for_make,
    IMFS_link,
    IMFS_unlink,
    IMFS_node_type,
    IMFS_mknod,
    IMFS_rmnod,
    IMFS_chown,
    IMFS_freenodinfo,
    IMFS_mount,
    IMFS_initialize,
    IMFS_unmount,
    IMFS_fsunmount,
    IMFS_utime,
    IMFS_evaluate_link,
    IMFS_symlink,
    IMFS_readlink
};

7.4.1.1. IMFS_evalpath()#

Corresponding Structure Element:

XXX

Arguments:

XXX

File:

XXX

Description:

XXX

7.4.1.2. IMFS_evalformake()#

Corresponding Structure Element:

XXX

Arguments:

XXX

File:

XXX

Description:

XXX

7.4.1.5. IMFS_node_type()#

Corresponding Structure Element:

IMFS_node_type()

Arguments:
rtems_filesystem_location_info_t    *pathloc        /* IN */
File:

imfs_ntype.c

Description:

This routine will locate the IMFS_jnode_t structure that holds ownership information for the selected node in the filesystem.

This structure is pointed to by pathloc->node_access.

The IMFS_jnode_t type element indicates one of the node types listed below:

  • RTEMS_FILESYSTEM_DIRECTORY

  • RTEMS_FILESYSTEM_DEVICE

  • RTEMS_FILESYSTEM_HARD_LINK

  • RTEMS_FILESYSTEM_MEMORY_FILE

7.4.1.6. IMFS_mknod()#

Corresponding Structure Element:

IMFS_mknod()

Arguments:
const char                          *token,        /* IN */
mode_t                               mode,         /* IN */
dev_t                                dev,          /* IN */
rtems_filesystem_location_info_t    *pathloc       /* IN/OUT */
File:

imfs_mknod.c

Description:

This routine will examine the mode argument to determine is we are trying to create a directory, regular file and a device node. The creation of other node types is not permitted and will cause an assert.

Memory space will be allocated for a jnode and the node will be set up according to the nodal type that was specified. The IMFS_create_node() function performs the allocation and setup of the node.

The only problem that is currently reported is the lack of memory when we attempt to allocate space for the jnode (ENOMEN).

7.4.1.7. IMFS_rmnod()#

Corresponding Structure Element:

XXX

Arguments:

XXX

File:

XXX

Description:

XXX

7.4.1.8. IMFS_chown()#

Corresponding Structure Element:

IMFS_chown()

Arguments:
rtems_filesystem_location_info_t    *pathloc        /* IN */
uid_t                                owner          /* IN */
gid_t                                group          /* IN */
File:

imfs_chown.c

Description:

This routine will locate the IMFS_jnode_t structure that holds ownership information for the selected node in the filesystem.

This structure is pointed to by pathloc->node_access.

The st_uid and st_gid fields of the node are then modified. Since this is a memory based filesystem, no further action is required to alter the ownership of the IMFS_jnode_t structure.

7.4.1.9. IMFS_freenod()#

Corresponding Structure Element:

IMFS_freenod()

Arguments:
rtems_filesystem_location_info_t      *pathloc       /* IN */
File:

imfs_free.c

Description:

This method is a private function to the IMFS. It is called by IMFS routines to free nodes that have been allocated. Examples of where this routine may be called from are unlink and rmnod.

Note: This routine should not be confused with the filesystem callback freenod. The IMFS allocates memory until the node no longer exists.

7.4.1.10. IMFS_freenodinfo()#

Corresponding Structure Element:

IMFS_freenodinfo()

Arguments:
rtems_filesystem_location_info_t      *pathloc       /* IN */
File:

imfs_free.c

Description:

The In-Memory File System does not need to allocate memory during the evaluate routines. Therefore, this routine simply routines PASS.

7.4.1.11. IMFS_mount()#

Corresponding Structure Element:

IMFS_mount()

Arguments:
rtems_filesystem_mount_table_entry_t   *mt_entry
File:

imfs_mount.c

Description:

This routine provides the filesystem specific processing required to mount a filesystem for the system that contains the mount point. It will determine if the point that we are trying to mount onto is a node of IMFS_DIRECTORY type.

If it is the node’s info element is altered so that the info.directory.mt_fs element points to the mount table chain entry that is associated with the mounted filesystem at this point. The info.directory.mt_fs element can be examined to determine if a filesystem is mounted at a directory. If it is NULL, the directory does not serve as a mount point. A non-NULL entry indicates that the directory does serve as a mount point and the value of info.directory.mt_fs can be used to locate the mount table chain entry that describes the filesystem mounted at this point.

7.4.1.12. IMFS_fsmount_me()#

Corresponding Structure Element:

IMFS_initialize()

Arguments:
rtems_filesystem_mount_table_entry_t   *mt_entry
File:

imfs_init.c

Description:

This function is provided with a filesystem to take care of the internal filesystem management details associated with mounting that filesystem under the RTEMS environment.

It is not responsible for the mounting details associated the filesystem containing the mount point.

The rtems_filesystem_mount_table_entry_t structure contains the key elements below:

rtems_filesystem_location_info_t         *mt_point_node,

This structure contains information about the mount point. This allows us to find the ops-table and the handling functions associated with the filesystem containing the mount point.

rtems_filesystem_location_info_t         *fs_root_node,

This structure contains information about the root node in the file system to be mounted. It allows us to find the ops-table and the handling functions associated with the filesystem to be mounted.

rtems_filesystem_options_t                 options,

Read only or read/write access

void                                         *fs_info,

This points to an allocated block of memory the will be used to hold any filesystem specific information of a global nature. This allocated region if important because it allows us to mount the same filesystem type more than once under the RTEMS system. Each instance of the mounted filesystem has its own set of global management information that is separate from the global management information associated with the other instances of the mounted filesystem type.

rtems_filesystem_limits_and_options_t    pathconf_info,

The table contains the following set of values associated with the mounted filesystem:

  • link_max

  • max_canon

  • max_input

  • name_max

  • path_max

  • pipe_buf

  • posix_async_io

  • posix_chown_restrictions

  • posix_no_trunc

  • posix_prio_io

  • posix_sync_io

  • posix_vdisable

These values are accessed with the pathconf() and the fpathconf () functions.

const char                                   *dev

The is intended to contain a string that identifies the device that contains the filesystem information. The filesystems that are currently implemented are memory based and don’t require a device specification.

If the mt_point_node.node_access is NULL then we are mounting the base file system.

The routine will create a directory node for the root of the IMFS file system.

The node will have read, write and execute permissions for owner, group and others.

The node’s name will be a null string.

A filesystem information structure(fs_info) will be allocated and initialized for the IMFS filesystem. The fs_info pointer in the mount table entry will be set to point the filesystem information structure.

The pathconf_info element of the mount table will be set to the appropriate table of path configuration constants ( IMFS_LIMITS_AND_OPTIONS ).

The fs_root_node structure will be filled in with the following:

  • pointer to the allocated root node of the filesystem

  • directory handlers for a directory node under the IMFS filesystem

  • OPS table functions for the IMFS

A 0 will be returned to the calling routine if the process succeeded, otherwise a 1 will be returned.

7.4.1.13. IMFS_unmount()#

Corresponding Structure Element:

IMFS_unmount()

Arguments:
rtems_filesystem_mount_table_entry_t   *mt_entry
File:

imfs_unmount.c

Description:

This routine allows the IMFS to unmount a filesystem that has been mounted onto a IMFS directory.

The mount entry mount point node access is verified to be a mounted directory. It’s mt_fs is set to NULL. This identifies to future calles into the IMFS that this directory node is no longer a mount point. Additionally, it will allow any directories that were hidden by the mounted system to again become visible.

7.4.1.14. IMFS_fsunmount()#

Corresponding Structure Element:

imfs_fsunmount()

Arguments:
rtems_filesystem_mount_table_entry_t   *mt_entry
File:

imfs_init.c

Description:

This method unmounts this instance of the IMFS file system. It is the counterpart to the IMFS_initialize routine. It is called by the generic code under the fsunmount_me callback.

All method loops finding the first encountered node with no children and removing the node from the tree, thus returning allocated resources. This is done until all allocated nodes are returned.

7.4.1.15. IMFS_utime()#

Corresponding Structure Element:

XXX

Arguments:

XXX

File:

XXX

Description:

XXX

7.4.2. Regular File Handler Table Functions#

Handler table functions are defined in a rtems_filesystem_file_handlers_r structure. It defines functions that are specific to a node type in a given filesystem. One table exists for each of the filesystem’s node types. The structure definition appears below. It is followed by general developmental information on each of the functions associated with regular files contained in this function management structure.

rtems_filesystem_file_handlers_r IMFS_memfile_handlers = {
    memfile_open,
    memfile_close,
    memfile_read,
    memfile_write,
    memfile_ioctl,
    memfile_lseek,
    IMFS_stat,
    IMFS_fchmod,
    memfile_ftruncate,
    NULL,                /* fpathconf */
    NULL,                /* fsync */
    IMFS_fdatasync,
    IMFS_fcntl
};

7.4.2.1. memfile_open() for Regular Files#

Corresponding Structure Element:

memfile_open()

Arguments:
rtems_libio_t   *iop,
const char      *pathname,
unsigned32       flag,
unsigned32       mode
File:

memfile.c

Description:

Currently this function is a shell. No meaningful processing is performed and a success code is always returned.

7.4.2.2. memfile_close() for Regular Files#

Corresponding Structure Element:

memfile_close()

Arguments:
rtems_libio_t     *iop
File:

memfile.c

Description:

This routine is a dummy for regular files under the base filesystem. It performs a capture of the IMFS_jnode_t pointer from the file control block and then immediately returns a success status.

7.4.2.3. memfile_read() for Regular Files#

Corresponding Structure Element:

memfile_read()

Arguments:
rtems_libio_t     *iop,
void              *buffer,
unsigned32         count
File:

memfile.c

Description:

This routine will determine the jnode that is associated with this file.

It will then call IMFS_memfile_read() with the jnode, file position index, buffer and transfer count as arguments.

IMFS_memfile_read() will do the following:

  • Verify that the jnode is associated with a memory file

  • Verify that the destination of the read is valid

  • Adjust the length of the read if it is too long

  • Acquire data from the memory blocks associated with the file

  • Update the access time for the data in the file

7.4.2.4. memfile_write() for Regular Files#

Corresponding Structure Element:

XXX

Arguments:

XXX

File:

XXX

Description:

XXX

7.4.2.5. memfile_ioctl() for Regular Files#

Corresponding Structure Element:

XXX

Arguments:
rtems_libio_t   *iop,
unsigned32       command,
void            *buffer
File:

memfile.c

Description:

The current code is a placeholder for future development. The routine returns a successful completion status.

7.4.2.6. memfile_lseek() for Regular Files#

Corresponding Structure Element:

Memfile_lseek()

Arguments:
rtems_libio_t     *iop,
off_t              offset,
int                whence
File:

memfile.c

Description:

This routine make sure that the memory based file is sufficiently large to allow for the new file position index.

The IMFS_memfile_extend() function is used to evaluate the current size of the memory file and allocate additional memory blocks if required by the new file position index. A success code is always returned from this routine.

7.4.2.7. IMFS_stat() for Regular Files#

Corresponding Structure Element:

IMFS_stat()

Arguments:
rtems_filesystem_location_info_t   *loc,
struct stat                        *buf
File:

imfs_stat.c

Description:

This routine actually performs status processing for both devices and regular files.

The IMFS_jnode_t structure is referenced to determine the type of node under the filesystem.

If the node is associated with a device, node information is extracted and transformed to set the st_dev element of the stat structure.

If the node is a regular file, the size of the regular file is extracted from the node.

This routine rejects other node types.

The following information is extracted from the node and placed in the stat structure:

  • st_mode

  • st_nlink

  • st_ino

  • st_uid

  • st_gid

  • st_atime

  • st_mtime

  • st_ctime

7.4.2.8. IMFS_fchmod() for Regular Files#

Corresponding Structure Element:

IMFS_fchmod()

Arguments:
rtems_libio_t     *iop
mode_t             mode
File:

imfs_fchmod.c

Description:

This routine will obtain the pointer to the IMFS_jnode_t structure from the information currently in the file control block.

Based on configuration the routine will acquire the user ID from a call to getuid() or from the IMFS_jnode_t structure.

It then checks to see if we have the ownership rights to alter the mode of the file. If the caller does not, an error code is returned.

An additional test is performed to verify that the caller is not trying to alter the nature of the node. If the caller is attempting to alter more than the permissions associated with user group and other, an error is returned.

If all the preconditions are met, the user, group and other fields are set based on the mode calling parameter.

7.4.2.9. memfile_ftruncate() for Regular Files#

Corresponding Structure Element:

XXX

Arguments:

XXX

File:

XXX

Description:

XXX

7.4.2.10. No pathconf() for Regular Files#

Corresponding Structure Element:

NULL

Arguments:

Not Implemented

File:

Not Implemented

Description:

Not Implemented

7.4.2.11. No fsync() for Regular Files#

Corresponding Structure Element:

XXX

Arguments:

XXX

File:

XXX

Description:

XXX

7.4.2.12. IMFS_fdatasync() for Regular Files#

Corresponding Structure Element:

XXX

Arguments:

XXX

File:

XXX

Description:

XXX

7.4.3. Directory Handler Table Functions#

Handler table functions are defined in a rtems_filesystem_file_handlers_r structure. It defines functions that are specific to a node type in a given filesystem. One table exists for each of the filesystem’s node types. The structure definition appears below. It is followed by general developmental information on each of the functions associated with directories contained in this function management structure.

rtems_filesystem_file_handlers_r IMFS_directory_handlers = {
    IMFS_dir_open,
    IMFS_dir_close,
    IMFS_dir_read,
    NULL,             /* write */
    NULL,             /* ioctl */
    IMFS_dir_lseek,
    IMFS_dir_fstat,
    IMFS_fchmod,
    NULL,             /* ftruncate */
    NULL,             /* fpathconf */
    NULL,             /* fsync */
    IMFS_fdatasync,
    IMFS_fcntl
};

7.4.3.1. IMFS_dir_open() for Directories#

Corresponding Structure Element:

imfs_dir_open()

Arguments:
rtems_libio_t  *iop,
const char     *pathname,
unsigned32      flag,
unsigned32      mode
File:

imfs_directory.c

Description:

This routine will look into the file control block to find the jnode that is associated with the directory.

The routine will verify that the node is a directory. If its not a directory an error code will be returned.

If it is a directory, the offset in the file control block will be set to 0. This allows us to start reading at the beginning of the directory.

7.4.3.2. IMFS_dir_close() for Directories#

Corresponding Structure Element:

imfs_dir_close()

Arguments:
rtems_libio_t     *iop
File:

imfs_directory.c

Description:

This routine is a dummy for directories under the base filesystem. It immediately returns a success status.

7.4.3.3. IMFS_dir_read() for Directories#

Corresponding Structure Element:

imfs_dir_read

Arguments:
rtems_libio_t  *iop,
void           *buffer,
unsigned32      count
File:

imfs_directory.c

Description:

This routine will read a fixed number of directory entries from the current directory offset. The number of directory bytes read will be returned from this routine.

7.4.3.4. No write() for Directories#

Corresponding Structure Element:

XXX

Arguments:

XXX

File:

XXX

Description:

XXX

7.4.3.5. No ioctl() for Directories#

Corresponding Structure Element:

ioctl

Arguments:

Not supported

File:

Not supported

Description:

XXX

7.4.3.6. IMFS_dir_lseek() for Directories#

Corresponding Structure Element:

imfs_dir_lseek()

Arguments:
rtems_libio_t      *iop,
off_t               offset,
int                 whence
File:

imfs_directory.c

Description:

This routine alters the offset in the file control block.

No test is performed on the number of children under the current open directory. The imfs_dir_read() function protects against reads beyond the current size to the directory by returning a 0 bytes transfered to the calling programs whenever the file position index exceeds the last entry in the open directory.

7.4.3.7. IMFS_dir_fstat() for Directories#

Corresponding Structure Element:

imfs_dir_fstat()

Arguments:
rtems_filesystem_location_info_t   *loc,
struct stat                        *buf
File:

imfs_directory.c

Description:

The node access information in the rtems_filesystem_location_info_t structure is used to locate the appropriate IMFS_jnode_t structure. The following information is taken from the IMFS_jnode_t structure and placed in the stat structure:

  • st_ino

  • st_mode

  • st_nlink

  • st_uid

  • st_gid

  • st_atime

  • st_mtime

  • st_ctime

The st_size field is obtained by running through the chain of directory entries and summing the sizes of the dirent structures associated with each of the children of the directory.

7.4.3.8. IMFS_fchmod() for Directories#

Corresponding Structure Element:

IMFS_fchmod()

Arguments:
rtems_libio_t     *iop
mode_t             mode
File:

imfs_fchmod.c

Description:

This routine will obtain the pointer to the IMFS_jnode_t structure from the information currently in the file control block.

Based on configuration the routine will acquire the user ID from a call to getuid() or from the IMFS_jnode_t structure.

It then checks to see if we have the ownership rights to alter the mode of the file. If the caller does not, an error code is returned.

An additional test is performed to verify that the caller is not trying to alter the nature of the node. If the caller is attempting to alter more than the permissions associated with user group and other, an error is returned.

If all the preconditions are met, the user, group and other fields are set based on the mode calling parameter.

7.4.3.9. No ftruncate() for Directories#

Corresponding Structure Element:

XXX

Arguments:

XXX

File:

XXX

Description:

XXX

7.4.3.10. No fpathconf() for Directories#

Corresponding Structure Element:

fpathconf

Arguments:

Not Implemented

File:

Not Implemented

Description:

Not Implemented

7.4.3.11. No fsync() for Directories#

Corresponding Structure Element:

XXX

Arguments:

XXX

File:

XXX

Description:

XXX

7.4.3.12. IMFS_fdatasync() for Directories#

Corresponding Structure Element:

XXX

Arguments:

XXX

File:

XXX

Description:

XXX

7.4.4. Device Handler Table Functions#

Handler table functions are defined in a rtems_filesystem_file_handlers_r structure. It defines functions that are specific to a node type in a given filesystem. One table exists for each of the filesystem’s node types. The structure definition appears below. It is followed by general developmental information on each of the functions associated with devices contained in this function management structure.

typedef struct {
    rtems_filesystem_open_t           open;
    rtems_filesystem_close_t          close;
    rtems_filesystem_read_t           read;
    rtems_filesystem_write_t          write;
    rtems_filesystem_ioctl_t          ioctl;
    rtems_filesystem_lseek_t          lseek;
    rtems_filesystem_fstat_t          fstat;
    rtems_filesystem_fchmod_t         fchmod;
    rtems_filesystem_ftruncate_t      ftruncate;
    rtems_filesystem_fpathconf_t      fpathconf;
    rtems_filesystem_fsync_t          fsync;
    rtems_filesystem_fdatasync_t      fdatasync;
} rtems_filesystem_file_handlers_r;

7.4.4.1. device_open() for Devices#

Corresponding Structure Element:

device_open()

Arguments:
rtems_libio_t     *iop,
const char        *pathname,
unsigned32         flag,
unsigned32         mode
File:

deviceio.c

Description:

This routine will use the file control block to locate the node structure for the device.

It will extract the major and minor device numbers from the jnode.

The major and minor device numbers will be used to make a rtems_io_open() function call to open the device driver. An argument list is sent to the driver that contains the file control block, flags and mode information.

7.4.4.2. device_close() for Devices#

Corresponding Structure Element:

device_close()

Arguments:
rtems_libio_t     *iop
File:

deviceio.c

Description:

This routine extracts the major and minor device driver numbers from the IMFS_jnode_t that is referenced in the file control block.

It also forms an argument list that contains the file control block.

A rtems_io_close() function call is made to close the device specified by the major and minor device numbers.

7.4.4.3. device_read() for Devices#

Corresponding Structure Element:

device_read()

Arguments:
rtems_libio_t     *iop,
void              *buffer,
unsigned32         count
File:

deviceio.c

Description:

This routine will extract the major and minor numbers for the device from the - jnode- associated with the file descriptor.

A rtems_io_read() call will be made to the device driver associated with the file descriptor. The major and minor device number will be sent as arguments as well as an argument list consisting of:

  • file control block

  • file position index

  • buffer pointer where the data read is to be placed

  • count indicating the number of bytes that the program wishes to read from the device

  • flags from the file control block

On return from the rtems_io_read() the number of bytes that were actually read will be returned to the calling program.

7.4.4.4. device_write() for Devices#

Corresponding Structure Element:

XXX

Arguments:

XXX

File:

XXX

Description:

XXX

7.4.4.5. device_ioctl() for Devices#

Corresponding Structure Element:

ioctl

Arguments:
rtems_libio_t     *iop,
unsigned32         command,
void              *buffer
File:

deviceio.c

Description:

This handler will obtain status information about a device.

The form of status is device dependent.

The rtems_io_control() function uses the major and minor number of the device to obtain the status information.

rtems_io_control() requires an rtems_libio_ioctl_args_t argument list which contains the file control block, device specific command and a buffer pointer to return the device status information.

The device specific command should indicate the nature of the information that is desired from the device.

After the rtems_io_control() is processed, the buffer should contain the requested device information.

If the device information is not obtained properly a -1 will be returned to the calling program, otherwise the ioctl_return value is returned.

7.4.4.6. device_lseek() for Devices#

Corresponding Structure Element:

device_lseek()

Arguments:
rtems_libio_t     *iop,
off_t              offset,
int                whence
File:

deviceio.c

Description:

At the present time this is a placeholder function. It always returns a successful status.

7.4.4.7. IMFS_stat() for Devices#

Corresponding Structure Element:

IMFS_stat()

Arguments:
rtems_filesystem_location_info_t   *loc,
struct stat                        *buf
File:

imfs_stat.c

Description:

This routine actually performs status processing for both devices and regular files.

The IMFS_jnode_t structure is referenced to determine the type of node under the filesystem.

If the node is associated with a device, node information is extracted and transformed to set the st_dev element of the stat structure.

If the node is a regular file, the size of the regular file is extracted from the node.

This routine rejects other node types.

The following information is extracted from the node and placed in the stat structure:

  • st_mode

  • st_nlink

  • st_ino

  • st_uid

  • st_gid

  • st_atime

  • st_mtime

  • st_ctime

7.4.4.8. IMFS_fchmod() for Devices#

Corresponding Structure Element:

IMFS_fchmod()

Arguments:
rtems_libio_t     *iop
mode_t             mode
File:

imfs_fchmod.c

Description:

This routine will obtain the pointer to the IMFS_jnode_t structure from the information currently in the file control block.

Based on configuration the routine will acquire the user ID from a call to getuid() or from the IMFS_jnode_t structure.

It then checks to see if we have the ownership rights to alter the mode of the file. If the caller does not, an error code is returned.

An additional test is performed to verify that the caller is not trying to alter the nature of the node. If the caller is attempting to alter more than the permissions associated with user group and other, an error is returned.

If all the preconditions are met, the user, group and other fields are set based on the mode calling parameter.

7.4.4.9. No ftruncate() for Devices#

Corresponding Structure Element:

XXX

Arguments:

XXX

File:

XXX

Description:

XXX

7.4.4.10. No fpathconf() for Devices#

Corresponding Structure Element:

fpathconf

Arguments:

Not Implemented

File:

Not Implemented

Description:

Not Implemented

7.4.4.11. No fsync() for Devices#

Corresponding Structure Element:

XXX

Arguments:

XXX

File:

XXX

Description:

XXX

7.4.4.12. No fdatasync() for Devices#

Not Implemented

Corresponding Structure Element:

XXX

Arguments:

XXX

File:

XXX

Description:

XXX

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