Pseudo-terminals, and what tmux and htop needed around them
- /dev/ptmx and /dev/pts/N: Unix98 pairs with a full line discipline, window sizes, job control and hangup (kernel/dev/pty.c). - The console speaks scroll regions, insert/delete line, SU/SD, RI/IND/NEL, DECSC/DECRC; swallows charset designations and private CSI sequences; and LF only returns the carriage under ONLCR. - setsid() drops the controlling terminal, so a pane's pty becomes its ctty. - pipe2() honours O_NONBLOCK and O_CLOEXEC (libevent's signal pipe). - File modes are stored and enforced: chmod, fchmod(at), umask, creation modes; /tmp is 1777. - /proc/stat has real user/system/idle; /proc/<pid>/task; kthread flag. - SO_PEERCRED, IOV_MAX 1024. - /proc/strace: name a program and its syscalls go to the kernel log. - World gains htop, btop, tmux, mc, ncdu, fastfetch, games, X toys, NetSurf. Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_01S1giNvrHTrPMPw7V6x1kQ4
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Nexoniarz
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28 changed files with 1577 additions and 47 deletions
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@ -18,6 +18,7 @@
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#include "fs/schfs.h" /* SCHFS_BLKSIZE, SCHFS_NAME_MAX — statfs reports them */
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#include "gfx/gfx.h" /* gfx_cols/gfx_rows — TIOCGWINSZ reports them */
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#include "dev/vt.h" /* the terminals the TIOC and VT_ ioctls act on */
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#include "dev/pty.h"
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#include "dev/pciuser.h"
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#include "dev/keymap.h" /* KB_*LAYOUT — the keyboard layout catalogue */
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#include "net/netuser.h"
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@ -83,6 +84,10 @@ linux_tty_rdev(uint32 major, uint32 minor)
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if (major == 1 && minor >= 11 && minor <= 16) return linux_makedev(4, minor - 10);
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if (major == 1 && minor == 10) return linux_makedev(5, 0);
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if (major == 1 && minor == 1) return linux_makedev(5, 1);
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// Pseudo-terminals, as Linux numbers them: ptmx (5, 2), slaves 136.
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if (major == PTMX_MAJOR) return linux_makedev(5, 2);
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if (major == PTS_MAJOR) return linux_makedev(136, minor);
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if (major == PTM_MAJOR) return linux_makedev(128, minor);
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return linux_makedev(major, minor);
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}
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@ -112,6 +117,10 @@ stati_linux(struct inode *ip, struct linux_stat *st)
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case T_SOCK: type_bits = LINUX_S_IFSOCK; perm_bits = 0755; break;
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default: type_bits = LINUX_S_IFREG; perm_bits = (ip->rwmode & 2) ? 0755 : 0555; break;
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}
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// A filesystem that keeps real permission bits -- SchFS does -- reports
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// those instead. tmux, ssh and gpg refuse a directory others can read.
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if (ip->mode)
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perm_bits = ip->mode & 07777;
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st->st_mode = type_bits | perm_bits;
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// Which device this node actually is. Left at zero until now, so every
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@ -264,9 +273,21 @@ path_toolong(const char *path)
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return 0;
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}
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// The mode argument of a Linux open/mkdir, or -1 from a native program, whose
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// calls have no such argument and leave whatever was in the register.
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static int
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linux_arg_mode(int n)
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{
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int mode;
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if (!myproc()->syscall_map)
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return -1;
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argint(n, &mode);
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return mode & 07777;
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}
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static struct inode*
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createat_x(int dirfd, char *path, short type, short major, short minor,
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int *err)
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int *err, int mode)
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{
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struct inode *ip, *dp;
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char name[VFS_NAME_MAX + 1];
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@ -320,6 +341,14 @@ createat_x(int dirfd, char *path, short type, short major, short minor,
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ilock(ip);
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ip->major = major; ip->minor = minor; ip->nlink = 1;
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ip->showmode = 1;
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// The permission bits asked for, less the umask -- or, from a caller that
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// has none to give, what open() and mkdir() would ask for. A symlink's
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// are 0777 on Linux whatever the umask, and nothing reads them.
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if (type == T_SYMLINK)
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ip->mode = 0777;
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else
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ip->mode = (uint)(mode >= 0 ? mode : type == T_DIR ? 0777 : 0666)
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& 07777 & ~myproc()->umask;
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iupdate(ip);
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if (type == T_DIR) {
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dp->nlink++;
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@ -343,7 +372,7 @@ createat_x(int dirfd, char *path, short type, short major, short minor,
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static struct inode*
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create(char *path, short type, short major, short minor)
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{
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return createat_x(AT_FDCWD, path, type, major, minor, 0);
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return createat_x(AT_FDCWD, path, type, major, minor, 0, -1);
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}
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// -----------------------------------------------------------------------
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@ -571,12 +600,16 @@ addr_t sys_pipe(void)
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return 0;
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}
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// The flags were ignored, and they are the point of pipe2: libevent makes its
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// signal pipe with O_NONBLOCK and drains it until EAGAIN, so the drain blocked
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// on the read after the last byte and tmux's client stopped dead.
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addr_t sys_pipe2(void)
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{
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addr_t fdarray;
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struct file *rf, *wf;
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int fd0, fd1;
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int fd0, fd1, flags;
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if (argaddr(0, &fdarray) < 0) return -1;
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argint(1, &flags);
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int *fds = (int*)user_ptr(fdarray, 2 * sizeof(int));
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if (!fds || pipealloc(&rf, &wf) < 0) return -1;
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fd0 = fd1 = -1;
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@ -585,6 +618,11 @@ addr_t sys_pipe2(void)
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fileclose(rf); fileclose(wf);
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return -1;
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}
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rf->nonblock = wf->nonblock = (flags & O_NONBLOCK) != 0;
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if (flags & O_CLOEXEC) {
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myproc()->ofile_flags[fd0] |= FD_CLOEXEC;
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myproc()->ofile_flags[fd1] |= FD_CLOEXEC;
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}
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fds[0] = fd0; fds[1] = fd1;
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return 0;
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}
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@ -642,7 +680,8 @@ addr_t sys_open(void)
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if (ip->type == T_DIR) { iunlockput(ip); end_op(); return -EISDIR; }
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} else
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ip = createat_x(AT_FDCWD, path,
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(omode & O_EXTENT) ? T_EXTENT : T_FILE, 0, 0, &cerr);
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(omode & O_EXTENT) ? T_EXTENT : T_FILE, 0, 0, &cerr,
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linux_arg_mode(2));
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// A refusal because the filesystem is read-only is not "no such file".
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// A shell prints the same sentence for every create failure, so
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// returning ENOENT here made writing to a snapshot look like a missing
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@ -660,6 +699,13 @@ addr_t sys_open(void)
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if (ip->type == T_DIR && (omode & O_ACCMODE) != O_RDONLY) { iunlockput(ip); end_op(); return -EISDIR; }
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if ((omode & O_TRUNC) && ip->type == T_FILE) itrunc(ip);
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}
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// /dev/ptmx: every open is a new pseudo-terminal, and the file holds its
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// master rather than the ptmx node. See kernel/dev/pty.c.
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if (ip->type == T_DEV && ip->major == PTMX_MAJOR) {
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struct inode *m = ptmx_open(ip);
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if (!m) { iunlockput(ip); end_op(); return -ENOSPC; }
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ip = m;
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}
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if (!(f = filealloc()) || (fd = fdalloc(f)) < 0) {
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if (f) fileclose(f);
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iunlockput(ip); end_op(); return -EMFILE;
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@ -699,7 +745,8 @@ addr_t sys_openat(void)
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if ((ip = open_existing(dirfd, path, omode)) != 0) {
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ilock(ip);
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if (ip->type == T_DIR) { iunlockput(ip); end_op(); return -EISDIR; }
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} else if (!(ip = createat_x(dirfd, path, T_FILE, 0, 0, &cerr))) {
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} else if (!(ip = createat_x(dirfd, path, T_FILE, 0, 0, &cerr,
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linux_arg_mode(3)))) {
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end_op();
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return cerr ? -cerr : -ENOENT;
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}
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@ -717,6 +764,13 @@ addr_t sys_openat(void)
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// depending on which entry point libc happened to call.
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if ((omode & O_TRUNC) && (ip->type == T_FILE || ip->type == T_EXTENT))
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itrunc(ip);
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// /dev/ptmx: every open is a new pseudo-terminal, and the file holds its
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// master rather than the ptmx node. See kernel/dev/pty.c.
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if (ip->type == T_DEV && ip->major == PTMX_MAJOR) {
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struct inode *m = ptmx_open(ip);
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if (!m) { iunlockput(ip); end_op(); return -ENOSPC; }
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ip = m;
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}
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if (!(f = filealloc()) || (fd = fdalloc(f)) < 0) {
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if (f) fileclose(f);
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iunlockput(ip); end_op(); return -EMFILE;
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@ -905,7 +959,8 @@ addr_t sys_mkdir(void)
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return -EEXIST;
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}
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int cerr = 0;
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if (!(ip = createat_x(AT_FDCWD, path, T_DIR, 0, 0, &cerr))) {
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if (!(ip = createat_x(AT_FDCWD, path, T_DIR, 0, 0, &cerr,
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linux_arg_mode(1)))) {
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end_op();
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return cerr ? -cerr : -ENOENT;
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}
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@ -948,7 +1003,7 @@ do_mknod(int dirfd, char *path, uint32 mode, uint64 dev)
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if (ex) { iput(ex); end_op(); return -EEXIST; }
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int cerr = 0;
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struct inode *ip = createat_x(dirfd, path, type, (short)major,
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(short)minor, &cerr);
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(short)minor, &cerr, (int)(mode & 07777));
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if (!ip) { end_op(); return cerr ? -cerr : -EEXIST; }
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iunlockput(ip); end_op();
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return 0;
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@ -1275,7 +1330,7 @@ do_symlink(int newdirfd, char *target, char *linkpath)
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return -EEXIST;
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}
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int cerr = 0;
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if (!(ip = createat_x(newdirfd, linkpath, T_SYMLINK, 0, 0, &cerr))) {
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if (!(ip = createat_x(newdirfd, linkpath, T_SYMLINK, 0, 0, &cerr, -1))) {
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end_op();
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return cerr ? -cerr : -ENOENT;
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}
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@ -1503,6 +1558,9 @@ addr_t sys_ioctl(void)
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if (is_dev && f->ip->major == AUDIO_MAJOR)
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return dsp_ioctl((int)request, argp);
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if (is_dev && (f->ip->major == PTM_MAJOR || f->ip->major == PTS_MAJOR))
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return pty_ioctl(f->ip, (uint)request, argp);
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int is_tty = (is_dev && f->ip->major == 1);
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if (!is_tty) {
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// -ENOTTY, not 0.
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@ -1776,8 +1834,50 @@ addr_t sys_ioctl(void)
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// createat() — every *at() syscall below uses them for dirfd resolution.)
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// chmod / fchmod / chown / fchown / lchown — stubs (no permission model yet).
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addr_t sys_chmod(void) { return 0; }
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addr_t sys_fchmod(void) { return 0; }
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// The new bits go in the inode and through iupdate to the filesystem. One
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// that keeps none (FAT) holds them only while the inode is cached, which is
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// as much as it can; there is no failure to report.
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static int
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chmod_inode(struct inode *ip, int mode)
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{
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if (fs_readonly(ip->dev))
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return -EROFS;
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ilock(ip);
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ip->mode = (uint)mode & 07777;
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if (ip->mode == 0)
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ip->mode = 01000000; // "no bits", as distinct from "never set"
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iupdate(ip);
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iunlock(ip);
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return 0;
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}
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addr_t sys_chmod(void)
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{
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char *path;
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int mode, err, r;
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struct inode *ip;
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if (argstr(0, &path) < 0) return -EFAULT;
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argint(1, &mode);
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begin_op();
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if (!(ip = at_nameif(AT_FDCWD, path, &err))) { end_op(); return -err; }
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r = chmod_inode(ip, mode);
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iput(ip);
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end_op();
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return r;
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}
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addr_t sys_fchmod(void)
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{
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struct file *f;
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int mode, r;
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if (argfd(0, 0, &f) < 0) return -EBADF;
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argint(1, &mode);
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if (f->type != FD_INODE || !f->ip) return 0;
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begin_op();
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r = chmod_inode(f->ip, mode);
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end_op();
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return r;
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}
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addr_t sys_chown(void) { return 0; }
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addr_t sys_fchown(void) { return 0; }
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addr_t sys_lchown(void) { return 0; }
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@ -2054,7 +2154,8 @@ addr_t sys_mkdirat(void)
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return -EEXIST;
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}
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int cerr = 0;
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if (!(ip = createat_x(dirfd, path, T_DIR, 0, 0, &cerr))) {
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if (!(ip = createat_x(dirfd, path, T_DIR, 0, 0, &cerr,
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linux_arg_mode(2)))) {
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end_op();
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return cerr ? -cerr : -ENOENT;
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}
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@ -2183,7 +2284,21 @@ addr_t sys_readlinkat(void)
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return got;
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}
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addr_t sys_fchmodat(void) { return 0; } // stub
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addr_t sys_fchmodat(void)
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{
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int dirfd, mode, err, r;
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char *path;
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struct inode *ip;
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argint(0, &dirfd);
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if (argstr(1, &path) < 0) return -EFAULT;
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argint(2, &mode);
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begin_op();
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if (!(ip = at_nameif(dirfd, path, &err))) { end_op(); return -err; }
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r = chmod_inode(ip, mode);
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iput(ip);
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end_op();
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return r;
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}
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addr_t sys_fchownat(void) { return 0; } // stub
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addr_t sys_faccessat(void)
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