The Atari Compendium/The Atari Compendium (Toad Computers) (1994).iso/files/prgtools/mint/filesy~1/mfs610s.zoo/docs/syscall.doc

Text File | 1994-05-12 | 7.8 KB | 213 lines

This file describes some of the syscalls and some special aspects of the
standard syscalls.

STAT (Fxattr)

Almost all the fields are relevant and not 'faked' unlike most of the
standard filesystems. There are a couple of minor exceptions. For V1
filesystems atime/adate and ctime/cdate fields are faked, they are
the same as mtime/mdate; these are not faked for V2 filesystems. The
nblocks field is faked by just assuming the file is continuous, this
will usually be correct; if the file is sparse however this will be
too high.

The 'dev' field is the drive with the standard form 0=A,1=B etc. The
field 'index' is the inode number, this is again valid: if two files
or file descriptors have the same inode and device numbers then they
are the same file, otherwise they are different.

If there are character or block special files on the device then the
field 'rdev' gets filled in appropriately.

DOPENDIR (DREADIR)

In normal mode you never get translated filenames, in addition the
long field is the inode number.

RENAME

You can 'move' directories with this call, as would be expected for
a U*ix like filesystem. This naturally moves all the contents of that
subtree as well. This call will not allow a directory to be moved inside
itself, as this would damage the filesystem (and is illegal anyway).

FDATIME

This is made fairly close to 'utimes', basically setting both atime/mtime
to the value specified and ctime to the current time. It can't change the
times for directories because MiNT blocks opening directories.

FATTR

This is largely faked, the fields aren't really valid for U*ix like
filesystems. Only the DIR/RDONLY bits have any meaning, and RDONLY
can be set as well.

VOLUME NAMES

Basically these don't exist. I suppose I could add support in some way if
there was any demand.

LINK/SYMLINK

As would be expected these are perfectly valid. LINK does not allow hard links
to directories, even by superuser basically because there is no real need since
symbolic links can do this and there would be no way to remove them.

UNLINK

Unlink behaves in a U*ix like manner with regard to open files. Basically you
can unlink() an open file and let all processes with it open read/write as
normal. When all processes close() the file (or exit which closes anyway) the
space used by the file is freed up.

You can *not* unlink directories, this would be too risky and isn't needed
anyway.

FSEEK

Minixfs allows the creation of sparse files in the usual way (seek past EOF and
write).

DCNTL CALLS

The Dcntl syscall has several options for minixfs filesystems. The 'standard'
calls FUTIME (set inode times) and FTRUNCATE (truncate file) exist as do their
Fcntl (ioctl) equivalents. However also inluded are several Minixfs specific
calls.

Opcode 0x100 MFS_VALID

This interprets the value of the additional argument as a long pointer, and
is stores the value MFS_MAGIC there. This is intended so that the path passed
to Dcntl can verified as being on a minixfs filesystem. MFS_MAGIC has the
value 0x1870431. Because of the possibility of other filesystems using the
same numbers for Dcntl functions with different purposes (though none do as
far as I know) MFS_VALID should always be called before using the other Minixfs
specific opcodes and MFS_MAGIC checked.

Opcode 0x101 MFS_SYNC

Synchronise *all* filesystems, basically write out internal buffers to disk.
Currently the filesystem internally sync()'s as well at various points, so
this call is not at present necessary before rebooting the system.

Opcode 0x102 MFS_CINVALID

Invalidate all cache entries for a given drive. This is used mainly internally.

Opcode 0x103 MFS_FINVALID

Invalidate all file descriptors on the given drive.

Opcode 0x104 MFS_INFO

This call basically returns some info about the Minixfs filesystem on which
the path resides. It interprets the value of the additional parameter as a
pointer to an mfs_info structure. This structure has the following form:

long total_inodes,total_zones;
long free_inodes,free_zones;
short version;
short incr;
long res1,res2,res3,res4;

(long=32 bits, short=16bits).

total_inodes and total_zones return the total number of inodes and zones
for the filesystem. Similarly free_inodes and free_zones show how many are
unused. A 'zone' is always 1K. version is 1 for V1 filesystems and 2 for
V2. incr is the directory increment. You can use this to determine the
maximum filename size with the formula incr*16-2. The MiNT syscall Dconf
can also be used for this purpose (see MiNT docs).

Opcode 0x106 MFS_IMODE

The extra paramater is interpreted as a long int. Its value is used to set
the mode of *all* the bits of the file pathname points to. Including the
type fields, thus you can change directories to files, and vice-versa.
This is again root only. Extreme caution is needed with this syscall: it
can do a lot of damage.

Opcode 0x107 MFS_GTRANS
Opcode 0x108 MFS_STRANS

This call gets and sets the translation modes for this device. Only the
superuser can do this. The extra parameter is interpreted as a long
pointer. The scope corresponds to the following values.

#define NONE    0
#define TOS     1
#define MINT    2
#define ALL     3

The 'type' is contained in groups of two bits. Bits 0-1 correspond to
search translation, bits 2-3 are directory translation, bits 4-5 are for
creation translation and bits 6-7 are for execute translation. All other
bits are currently ignored and should be set to zero.

Opcode 0x10a MFS_IADDR

The argument is a long pointer which will have the start address of Minixfs
placed in it. If Minixfs has crashed then using this address along with the
symbol table (or a suitable debugger) allows the precise point of the crash
to be determined.

Opcode 0x10b MFS_UPDATE

This controls the update daemon. If no daemon is running (e.g. not Turbo mode)
then this function returns -1. Otherwise the argument is a long which is
interpreted as follows.

0x0: Return 1 if daemon suspended, 0 if running.
0x1: Suspend execution of the daemon.
0x2: Resume execution of daemon.
0x3: Return the process id (pid) of the daemon (returns -1 if daemon not used)

Opcode 0x10c MFS_MOUNT

This is a bit experimental at present. It is used to mount one Minixfs
filesystem on another and may go away some day if the kernel implements
this (which is where it should really be). 'arg' is a pointer to the
following structure:

unsigned int dev;
long flags;
long reserved[4];

dev is the device to mount (the path to Dcntl gives the path to mount on).
flags is unused at present and should be set to zero. The reserved fields
are also unused at present. The Dcntl path must be a directory other than
the root directory. The filesystem of device 'dev' must not have any filesytems
mounted on it already.

Opcode 0x10d MFS_UMOUNT

The filesystem the Dcntl path is on is umounted.

Opcode 0x10e MFS_LOPEN

arg points to the following structure:

long limit;
unsigned int ilist[SIZE];

The field 'limit' should be set to the value of SIZE (the size of the ilist
array). After this call the inode numbers of all open files on the Dcntl path
filesystem are entered into the ilist array, followed by a zero terminator.
If there isn't enough room in the array, it is truncated and ERANGE returned.

Opcode 0x10f MFS_MKNOD

arg is a long. The low word is a mode parameter which is the full mode of
a character or block special file mode. The high word is the major/minor
device numbers of the file. The Dcntl path is the path to create.

NOTE ON FILENAME TRANSLATION

Using minixfs filesystems you should always use the Dopendir etc. MiNT calls
in normal mode. This way you never get translated filenames. You can use the
Dconf or the MFS_INFO Dcntl syscalls to get the maximum filename length (if
needed).