9p.c

这是一个同样来自贝尔实验室的和UNIX有着渊源的操作系统, 其简洁的设计和实现易于我们学习和理解

#include "stdinc.h"

#include "9.h"

enum {
	OMODE		= 0x7,		/* Topen/Tcreate mode */
};

enum {
	PermX		= 1,
	PermW		= 2,
	PermR		= 4,
};

static char EPermission[] = "permission denied";

static int
permFile(File* file, Fid* fid, int perm)
{
	char *u;
	DirEntry de;

	if(!fileGetDir(file, &de))
		return -1;

	/*
	 * User none only gets other permissions.
	 */
	if(strcmp(fid->uname, unamenone) != 0){
		/*
		 * There is only one uid<->uname mapping
		 * and it's already cached in the Fid, but
		 * it might have changed during the lifetime
		 * if this Fid.
		 */
		if((u = unameByUid(de.uid)) != nil){
			if(strcmp(fid->uname, u) == 0 && ((perm<<6) & de.mode)){
				vtMemFree(u);
				deCleanup(&de);
				return 1;
			}
			vtMemFree(u);
		}
		if(groupMember(de.gid, fid->uname) && ((perm<<3) & de.mode)){
			deCleanup(&de);
			return 1;
		}
	}
	if(perm & de.mode){
		if(perm == PermX && (de.mode & ModeDir)){
			deCleanup(&de);
			return 1;
		}
		if(!groupMember(uidnoworld, fid->uname)){
			deCleanup(&de);
			return 1;
		}
	}
	if(fsysNoPermCheck(fid->fsys) || (fid->con->flags&ConNoPermCheck)){
		deCleanup(&de);
		return 1;
	}
	vtSetError(EPermission);

	deCleanup(&de);
	return 0;
}

static int
permFid(Fid* fid, int p)
{
	return permFile(fid->file, fid, p);
}

static int
permParent(Fid* fid, int p)
{
	int r;
	File *parent;

	parent = fileGetParent(fid->file);
	r = permFile(parent, fid, p);
	fileDecRef(parent);

	return r;
}

int
validFileName(char* name)
{
	char *p;

	if(name == nil || name[0] == '\0'){
		vtSetError("no file name");
		return 0;
	}
	if(name[0] == '.'){
		if(name[1] == '\0' || (name[1] == '.' && name[2] == '\0')){
			vtSetError(". and .. illegal as file name");
			return 0;
		}
	}

	for(p = name; *p != '\0'; p++){
		if((*p & 0xFF) < 040){
			vtSetError("bad character in file name");
			return 0;
		}
	}

	return 1;
}

static int
rTwstat(Msg* m)
{
	Dir dir;
	Fid *fid;
	ulong mode, oldmode;
	DirEntry de;
	char *gid, *strs, *uid;
	int gl, op, retval, tsync, wstatallow;

	if((fid = fidGet(m->con, m->t.fid, FidFWlock)) == nil)
		return 0;

	gid = uid = nil;
	retval = 0;

	if(strcmp(fid->uname, unamenone) == 0 || (fid->qid.type & QTAUTH)){
		vtSetError(EPermission);
		goto error0;
	}
	if(fileIsRoFs(fid->file) || !groupWriteMember(fid->uname)){
		vtSetError("read-only filesystem");
		goto error0;
	}

	if(!fileGetDir(fid->file, &de))
		goto error0;

	strs = vtMemAlloc(m->t.nstat);
	if(convM2D(m->t.stat, m->t.nstat, &dir, strs) == 0){
		vtSetError("wstat -- protocol botch");
		goto error;
	}

	/*
	 * Run through each of the (sub-)fields in the provided Dir
	 * checking for validity and whether it's a default:
	 * .type, .dev and .atime are completely ignored and not checked;
	 * .qid.path, .qid.vers and .muid are checked for validity but
	 * any attempt to change them is an error.
	 * .qid.type/.mode, .mtime, .name, .length, .uid and .gid can
	 * possibly be changed.
	 *
	 * 'Op' flags there are changed fields, i.e. it's not a no-op.
	 * 'Tsync' flags all fields are defaulted.
	 */
	tsync = 1;
	if(dir.qid.path != ~0){
		if(dir.qid.path != de.qid){
			vtSetError("wstat -- attempt to change qid.path");
			goto error;
		}
		tsync = 0;
	}
	if(dir.qid.vers != ~0){
		if(dir.qid.vers != de.mcount){
			vtSetError("wstat -- attempt to change qid.vers");
			goto error;
		}
		tsync = 0;
	}
	if(dir.muid != nil && *dir.muid != '\0'){
		if((uid = uidByUname(dir.muid)) == nil){
			vtSetError("wstat -- unknown muid");
			goto error;
		}
		if(strcmp(uid, de.mid) != 0){
			vtSetError("wstat -- attempt to change muid");
			goto error;
		}
		vtMemFree(uid);
		uid = nil;
		tsync = 0;
	}

	/*
	 * Check .qid.type and .mode agree if neither is defaulted.
	 */
	if(dir.qid.type != (uchar)~0 && dir.mode != ~0){
		if(dir.qid.type != ((dir.mode>>24) & 0xFF)){
			vtSetError("wstat -- qid.type/mode mismatch");
			goto error;
		}
	}

	op = 0;

	oldmode = de.mode;
	if(dir.qid.type != (uchar)~0 || dir.mode != ~0){
		/*
		 * .qid.type or .mode isn't defaulted, check for unknown bits.
		 */
		if(dir.mode == ~0)
			dir.mode = (dir.qid.type<<24)|(de.mode & 0777);
		if(dir.mode & ~(DMDIR|DMAPPEND|DMEXCL|DMTMP|0777)){
			vtSetError("wstat -- unknown bits in qid.type/mode");
			goto error;
		}

		/*
		 * Synthesise a mode to check against the current settings.
		 */
		mode = dir.mode & 0777;
		if(dir.mode & DMEXCL)
			mode |= ModeExclusive;
		if(dir.mode & DMAPPEND)
			mode |= ModeAppend;
		if(dir.mode & DMDIR)
			mode |= ModeDir;
		if(dir.mode & DMTMP)
			mode |= ModeTemporary;

		if((de.mode^mode) & ModeDir){
			vtSetError("wstat -- attempt to change directory bit");
			goto error;
		}

		if((de.mode & (ModeAppend|ModeExclusive|ModeTemporary|0777)) != mode){
			de.mode &= ~(ModeAppend|ModeExclusive|ModeTemporary|0777);
			de.mode |= mode;
			op = 1;
		}
		tsync = 0;
	}

	if(dir.mtime != ~0){
		if(dir.mtime != de.mtime){
			de.mtime = dir.mtime;
			op = 1;
		}
		tsync = 0;
	}

	if(dir.length != ~0){
		if(dir.length != de.size){
			/*
			 * Cannot change length on append-only files.
			 * If we're changing the append bit, it's okay.
			 */
			if(de.mode & oldmode & ModeAppend){
				vtSetError("wstat -- attempt to change length of append-only file");
				goto error;
			}
			if(de.mode & ModeDir){
				vtSetError("wstat -- attempt to change length of directory");
				goto error;
			}
			de.size = dir.length;
			op = 1;
		}
		tsync = 0;
	}

	/*
	 * Check for permission to change .mode, .mtime or .length,
	 * must be owner or leader of either group, for which test gid
	 * is needed; permission checks on gid will be done later.
	 */
	if(dir.gid != nil && *dir.gid != '\0'){
		if((gid = uidByUname(dir.gid)) == nil){
			vtSetError("wstat -- unknown gid");
			goto error;
		}
		tsync = 0;
	}
	else
		gid = vtStrDup(de.gid);

	wstatallow = (fsysWstatAllow(fid->fsys) || (m->con->flags&ConWstatAllow));

	/*
	 * 'Gl' counts whether neither, one or both groups are led.
	 */
	gl = groupLeader(gid, fid->uname) != 0;
	gl += groupLeader(de.gid, fid->uname) != 0;

	if(op && !wstatallow){
		if(strcmp(fid->uid, de.uid) != 0 && !gl){
			vtSetError("wstat -- not owner or group leader");
			goto error;
		}
	}

	/*
	 * Check for permission to change group, must be
	 * either owner and in new group or leader of both groups.
	 * If gid is nil here then
	 */
	if(strcmp(gid, de.gid) != 0){
		if(!wstatallow
		&& !(strcmp(fid->uid, de.uid) == 0 && groupMember(gid, fid->uname))
		&& !(gl == 2)){
			vtSetError("wstat -- not owner and not group leaders");
			goto error;
		}
		vtMemFree(de.gid);
		de.gid = gid;
		gid = nil;
		op = 1;
		tsync = 0;
	}

	/*
	 * Rename.
	 * Check .name is valid and different to the current.
	 * If so, check write permission in parent.
	 */
	if(dir.name != nil && *dir.name != '\0'){
		if(!validFileName(dir.name))
			goto error;
		if(strcmp(dir.name, de.elem) != 0){
			if(permParent(fid, PermW) <= 0)
				goto error;
			vtMemFree(de.elem);
			de.elem = vtStrDup(dir.name);
			op = 1;
		}
		tsync = 0;
	}

	/*
	 * Check for permission to change owner - must be god.
	 */
	if(dir.uid != nil && *dir.uid != '\0'){
		if((uid = uidByUname(dir.uid)) == nil){
			vtSetError("wstat -- unknown uid");
			goto error;
		}
		if(strcmp(uid, de.uid) != 0){
			if(!wstatallow){
				vtSetError("wstat -- not owner");
				goto error;
			}
			if(strcmp(uid, uidnoworld) == 0){
				vtSetError(EPermission);
				goto error;
			}
			vtMemFree(de.uid);
			de.uid = uid;
			uid = nil;
			op = 1;
		}
		tsync = 0;
	}

	if(op)
		retval = fileSetDir(fid->file, &de, fid->uid);
	else
		retval = 1;

	if(tsync){
		/*
		 * All values were defaulted,
		 * make the state of the file exactly what it
		 * claims to be before returning...
		 */
		USED(tsync);
	}

error:
	deCleanup(&de);
	vtMemFree(strs);
	if(gid != nil)
		vtMemFree(gid);
	if(uid != nil)
		vtMemFree(uid);
error0:
	fidPut(fid);
	return retval;
};

static int
rTstat(Msg* m)
{
	Dir dir;
	Fid *fid;
	DirEntry de;

	if((fid = fidGet(m->con, m->t.fid, 0)) == nil)
		return 0;
	if(fid->qid.type & QTAUTH){
		memset(&dir, 0, sizeof(Dir));
		dir.qid = fid->qid;
		dir.mode = DMAUTH;
		dir.atime = time(0L);
		dir.mtime = dir.atime;
		dir.length = 0;
		dir.name = "#¿";
		dir.uid = fid->uname;
		dir.gid = fid->uname;
		dir.muid = fid->uname;

		if((m->r.nstat = convD2M(&dir, m->data, m->con->msize)) == 0){
			vtSetError("stat QTAUTH botch");
			fidPut(fid);
			return 0;
		}
		m->r.stat = m->data;

		fidPut(fid);
		return 1;
	}
	if(!fileGetDir(fid->file, &de)){
		fidPut(fid);
		return 0;
	}
	fidPut(fid);

	/*
	 * TODO: optimise this copy (in convS2M) away somehow.
	 * This pettifoggery with m->data will do for the moment.
	 */
	m->r.nstat = dirDe2M(&de, m->data, m->con->msize);
	m->r.stat = m->data;
	deCleanup(&de);

	return 1;
}

static int
_rTclunk(Fid* fid, int remove)
{
	int rok;

	if(fid->excl)
		exclFree(fid);

	rok = 1;
	if(remove && !(fid->qid.type & QTAUTH)){
		if((rok = permParent(fid, PermW)) > 0)
			rok = fileRemove(fid->file, fid->uid);
	}
	fidClunk(fid);

	return rok;
}

static int
rTremove(Msg* m)
{
	Fid *fid;

	if((fid = fidGet(m->con, m->t.fid, FidFWlock)) == nil)
		return 0;
	return _rTclunk(fid, 1);
}

static int
rTclunk(Msg* m)
{
	Fid *fid;

	if((fid = fidGet(m->con, m->t.fid, FidFWlock)) == nil)
		return 0;
	_rTclunk(fid, (fid->open & FidORclose));

	return 1;
}

static int
rTwrite(Msg* m)
{
	Fid *fid;
	int count, n;

	if((fid = fidGet(m->con, m->t.fid, 0)) == nil)
		return 0;
	if(!(fid->open & FidOWrite)){
		vtSetError("fid not open for write");
		goto error;
	}

	count = m->t.count;
	if(count < 0 || count > m->con->msize-IOHDRSZ){
		vtSetError("write count too big");
		goto error;
	}
	if(m->t.offset < 0){
		vtSetError("write offset negative");
		goto error;
	}
	if(fid->excl != nil && !exclUpdate(fid))
		goto error;

	if(fid->qid.type & QTDIR){
		vtSetError("is a directory");
		goto error;
	}
	else if(fid->qid.type & QTAUTH)
		n = authWrite(fid, m->t.data, count);
	else
		n = fileWrite(fid->file, m->t.data, count, m->t.offset, fid->uid);
	if(n < 0)
		goto error;


	m->r.count = n;

	fidPut(fid);
	return 1;

error:
	fidPut(fid);
	return 0;
}

static int
rTread(Msg* m)
{
	Fid *fid;
	uchar *data;
	int count, n;

	if((fid = fidGet(m->con, m->t.fid, 0)) == nil)
		return 0;
	if(!(fid->open & FidORead)){
		vtSetError("fid not open for read");
		goto error;
	}

	count = m->t.count;
	if(count < 0 || count > m->con->msize-IOHDRSZ){
		vtSetError("read count too big");
		goto error;
	}
	if(m->t.offset < 0){
		vtSetError("read offset negative");
		goto error;
	}
	if(fid->excl != nil && !exclUpdate(fid))
		goto error;

	/*
	 * TODO: optimise this copy (in convS2M) away somehow.
	 * This pettifoggery with m->data will do for the moment.
	 */
	data = m->data+IOHDRSZ;
	if(fid->qid.type & QTDIR)
		n = dirRead(fid, data, count, m->t.offset);
	else if(fid->qid.type & QTAUTH)
		n = authRead(fid, data, count);
	else
		n = fileRead(fid->file, data, count, m->t.offset);
	if(n < 0)
		goto error;

	m->r.count = n;
	m->r.data = (char*)data;

	fidPut(fid);
	return 1;

error:
	fidPut(fid);
	return 0;
}

static int
rTcreate(Msg* m)
{
	Fid *fid;
	File *file;
	ulong mode;
	int omode, open, perm;

	if((fid = fidGet(m->con, m->t.fid, FidFWlock)) == nil)
		return 0;
	if(fid->open){
		vtSetError("fid open for I/O");
		goto error;
	}
	if(fileIsRoFs(fid->file) || !groupWriteMember(fid->uname)){
		vtSetError("read-only filesystem");
		goto error;
	}