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subshell.c

/***********************************************************************
*                                                                      *
*               This software is part of the ast package               *
*           Copyright (c) 1982-2007 AT&T Knowledge Ventures            *
*                      and is licensed under the                       *
*                  Common Public License, Version 1.0                  *
*                      by AT&T Knowledge Ventures                      *
*                                                                      *
*                A copy of the License is available at                 *
*            http://www.opensource.org/licenses/cpl1.0.txt             *
*         (with md5 checksum 059e8cd6165cb4c31e351f2b69388fd9)         *
*                                                                      *
*              Information and Software Systems Research               *
*                            AT&T Research                             *
*                           Florham Park NJ                            *
*                                                                      *
*                  David Korn <dgk@research.att.com>                   *
*                                                                      *
***********************************************************************/
#pragma prototyped
/*
 *   Create and manage subshells avoiding forks when possible
 *
 *   David Korn
 *   AT&T Labs
 *
 */

#include    "defs.h"
#include    <ls.h>
#include    "io.h"
#include    "fault.h"
#include    "shnodes.h"
#include    "shlex.h"
#include    "jobs.h"
#include    "variables.h"
#include    "path.h"

#ifndef PIPE_BUF
#   define PIPE_BUF     512
#endif

/*
 * Note that the following structure must be the same
 * size as the Dtlink_t structure
 */
struct Link
{
      struct Link *next;
      Namval_t    *node;
};

/*
 * The following structure is used for command substitution and (...)
 */
static struct subshell
{
      struct subshell   *prev;      /* previous subshell data */
      struct subshell   *pipe;      /* subshell where output goes to pipe on fork */
      Dt_t        *var; /* variable table at time of subshell */
      struct Link *svar;      /* save shell variable table */
      Dt_t        *sfun;      /* function scope for subshell */
      Dt_t        *salias;/* alias scope for subshell */
#ifdef PATH_BFPATH
      Pathcomp_t  *pathlist; /* for PATH variable */
#endif
#if (ERROR_VERSION >= 20030214L)
      struct Error_context_s *errcontext;
#else
      struct errorcontext *errcontext;
#endif
      Shopt_t           options;/* save shell options */
      pid_t       subpid;     /* child process id */
      Sfio_t*     saveout;/*saved standard output */
      char        *pwd; /* present working directory */
      const char  *shpwd;     /* saved pointer to sh.pwd */
      void        *jobs;      /* save job info */
      mode_t            mask; /* saved umask */
      short       tmpfd;      /* saved tmp file descriptor */
      short       pipefd;     /* read fd if pipe is created */
      char        jobcontrol;
      char        monitor;
      unsigned char     fdstatus;
      int         fdsaved; /* bit make for saved files */
      int         bckpid;
} *subshell_data;

static int subenv;

/*
 * This routine will turn the sftmp() file into a real /tmp file or pipe
 * if the /tmp file create fails
 */
void  sh_subtmpfile(void)
{
      if(sfset(sfstdout,0,0)&SF_STRING)
      {
            register int fd;
            register struct checkpt *pp = (struct checkpt*)sh.jmplist;
            register struct subshell *sp = subshell_data->pipe;
            /* save file descriptor 1 if open */
            if((sp->tmpfd = fd = fcntl(1,F_DUPFD,10)) >= 0)
            {
                  fcntl(fd,F_SETFD,FD_CLOEXEC);
                  sh.fdstatus[fd] = sh.fdstatus[1]|IOCLEX;
                  close(1);
            }
            else if(errno!=EBADF)
                  errormsg(SH_DICT,ERROR_system(1),e_toomany);
            /* popping a discipline forces a /tmp file create */
            sfdisc(sfstdout,SF_POPDISC);
            if((fd=sffileno(sfstdout))<0)
            {
                  /* unable to create the /tmp file so use a pipe */
                  int fds[2];
                  Sfoff_t off;
                  sh_pipe(fds);
                  sp->pipefd = fds[0];
                  sh_fcntl(sp->pipefd,F_SETFD,FD_CLOEXEC);
                  /* write the data to the pipe */
                  if(off = sftell(sfstdout))
                        write(fds[1],sfsetbuf(sfstdout,(Void_t*)sfstdout,0),(size_t)off);
                  sfclose(sfstdout);
                  if((sh_fcntl(fds[1],F_DUPFD, 1)) != 1)
                        errormsg(SH_DICT,ERROR_system(1),e_file+4);
                  sh_close(fds[1]);
            }
            else
            {
                  sh.fdstatus[fd] = IOREAD|IOWRITE;
                  sfsync(sfstdout);
                  if(fd==1)
                        fcntl(1,F_SETFD,0);
                  else
                  {
                        sfsetfd(sfstdout,1);
                        sh.fdstatus[1] = sh.fdstatus[fd];
                        sh.fdstatus[fd] = IOCLOSE;
                  }
            }
            sh_iostream(1);
            sfset(sfstdout,SF_SHARE|SF_PUBLIC,1);
            sfpool(sfstdout,sh.outpool,SF_WRITE);
            if(pp && pp->olist  && pp->olist->strm == sfstdout)
                  pp->olist->strm = 0;
      }
}

/*
 * This routine creates a temp file if necessary and creates a subshell.
 * The parent routine longjmps back to sh_subshell()
 * The child continues possibly with its standard output replaced by temp file
 */
void sh_subfork(void)
{
      register struct subshell *sp = subshell_data;
      pid_t pid;
      /* see whether inside $(...) */
      if(sp->pipe)
            sh_subtmpfile();
      if(pid = sh_fork(0,NIL(int*)))
      {
            /* this is the parent part of the fork */
            if(sp->subpid==0)
                  sp->subpid = pid;
            siglongjmp(*sh.jmplist,SH_JMPSUB);
      }
      else
      {
            int16_t subshell;
            /* this is the child part of the fork */
            /* setting subpid to 1 causes subshell to exit when reached */
            sh_onstate(SH_FORKED);
            sh_onstate(SH_NOLOG);
            sh_offstate(SH_MONITOR);
            subshell_data = 0;
            subshell = sh.subshell = 0;
            nv_putval(SH_SUBSHELLNOD, (char*)&subshell, NV_INT16);
            sp->subpid=0;
      }
}

/*
 * This routine will make a copy of the given node in the
 * layer created by the most recent subshell_fork if the
 * node hasn't already been copied
 */
Namval_t *sh_assignok(register Namval_t *np,int add)
{
      register Namval_t *mp;
      register struct Link *lp;
      register struct subshell *sp = (struct subshell*)subshell_data;
      int save;
      /* don't bother with this */
      if(!sp->shpwd || (nv_isnull(np) && !add))
            return(np);
      /* don't bother to save if in newer scope */
      if(nv_search((char*)np,sp->var,HASH_BUCKET)!=np)
            return(np);
      for(lp=subshell_data->svar; lp; lp = lp->next)
      {
            if(lp->node==np)
                  return(np);
      }
      mp =  newof(0,Namval_t,1,0);
      lp = (struct Link*)mp;
      lp->node = np;
      lp->next = subshell_data->svar; 
      subshell_data->svar = lp;
      save = sh.subshell;
      sh.subshell = 0;;
      mp->nvname = np->nvname;
      nv_clone(np,mp,NV_NOFREE);
      sh.subshell = save;
      return(np);
}

/*
 * restore the variables
 */
static void nv_restore(struct subshell *sp)
{
      register struct Link *lp, *lq;
      register Namval_t *mp, *np;
      const char *save = sp->shpwd;
      sp->shpwd = 0;    /* make sure sh_assignok doesn't save with nv_unset() */
      for(lp=sp->svar; lp; lp=lq)
      {
            np = (Namval_t*)lp;
            mp = lp->node;
            lq = lp->next;
            if(nv_isarray(mp))
                   nv_putsub(mp,NIL(char*),ARRAY_SCAN);
            _nv_unset(mp,NV_RDONLY);
            nv_setsize(mp,nv_size(np));
            if(!nv_isattr(np,NV_MINIMAL) || nv_isattr(np,NV_EXPORT))
                  mp->nvenv = np->nvenv;
            mp->nvfun = np->nvfun;
            mp->nvflag = np->nvflag;
            if(nv_cover(mp))
                  nv_putval(mp, np->nvalue.cp,0);
            else
                  mp->nvalue.cp = np->nvalue.cp;
            np->nvfun = 0;
            if(nv_isattr(mp,NV_EXPORT))
            {
                  char *name = nv_name(mp);
                  sh_envput(sh.env,mp);
                  if(*name=='_' && strcmp(name,"_AST_FEATURES")==0)
                        astconf(NiL, NiL, NiL);
            }
            else if(nv_isattr(np,NV_EXPORT))
                  env_delete(sh.env,nv_name(mp));
            free((void*)np);
      }
      sp->shpwd=save;
}

/*
 * return pointer to alias tree
 * create new one if in a subshell and one doesn't exist and create is non-zero
 */
Dt_t *sh_subaliastree(int create)
{
      register struct subshell *sp = subshell_data;
      if(!sp || sh.curenv==0)
            return(sh.alias_tree);
      if(!sp->salias && create)
      {
            sp->salias = dtopen(&_Nvdisc,Dtoset);
            dtview(sp->salias,sh.alias_tree);
            sh.alias_tree = sp->salias;
      }
      return(sp->salias);
}

/*
 * return pointer to function tree
 * create new one if in a subshell and one doesn't exist and create is non-zero
 */
Dt_t *sh_subfuntree(int create)
{
      register struct subshell *sp = subshell_data;
      if(!sp || sh.curenv==0)
            return(sh.fun_tree);
      if(!sp->sfun && create)
      {
            sp->sfun = dtopen(&_Nvdisc,Dtoset);
            dtview(sp->sfun,sh.fun_tree);
            sh.fun_tree = sp->sfun;
      }
      return(sp->sfun);
}

static void table_unset(register Dt_t *root)
{
      register Namval_t *np,*nq;
      for(np=(Namval_t*)dtfirst(root);np;np=nq)
      {
            _nv_unset(np,NV_RDONLY);
            nq = (Namval_t*)dtnext(root,np);
            dtdelete(root,np);
            free((void*)np);
      }
}

int sh_subsavefd(register int fd)
{
      register struct subshell *sp = subshell_data;
      register int old=0;
      if(sp)
      {
            old = !(sp->fdsaved&(1<<(fd-1)));
            sp->fdsaved |= (1<<(fd-1));
      }
      return(old);
}

/*
 * Run command tree <t> in a virtual sub-shell
 * If comsub is not null, then output will be placed in temp file (or buffer)
 * If comsub is not null, the return value will be a stream consisting of
 * output of command <t>.  Otherwise, NULL will be returned.
 */

Sfio_t *sh_subshell(Shnode_t *t, int flags, int comsub)
{
      Shell_t *shp = &sh;
      struct subshell sub_data;
      register struct subshell *sp = &sub_data;
      int jmpval,nsig;
      int savecurenv = shp->curenv;
      int savejobpgid = job.curpgid;
      int16_t subshell;
      char *savsig;
      Sfio_t *iop=0;
      struct checkpt buff;
      struct sh_scoped savst;
      struct dolnod   *argsav=0;
      memset((char*)sp, 0, sizeof(*sp));
      sfsync(shp->outpool);
      argsav = sh_arguse();
      if(shp->curenv==0)
      {
            subshell_data=0;
            subenv = 0;
      }
      shp->curenv = ++subenv;
      job.curpgid = 0;
      savst = shp->st;
      sh_pushcontext(&buff,SH_JMPSUB);
      subshell = shp->subshell+1;
      nv_putval(SH_SUBSHELLNOD, (char*)&subshell, NV_INT16);
      shp->subshell = subshell;
      sp->prev = subshell_data;
      subshell_data = sp;
      sp->errcontext = &buff.err;
      sp->var = shp->var_tree;
      sp->options = shp->options;
      sp->jobs = job_subsave();
#ifdef PATH_BFPATH
      /* make sure initialization has occurred */ 
      if(!shp->pathlist)
            path_get(".");
      sp->pathlist = path_dup((Pathcomp_t*)shp->pathlist);
#endif
      if(!shp->pwd)
            path_pwd(0);
      sp->bckpid = shp->bckpid;
      if(!comsub || (comsub==1 && !sh_isoption(SH_SUBSHARE)))
      {
            sp->shpwd = shp->pwd;
            sp->pwd = (shp->pwd?strdup(shp->pwd):0);
            sp->mask = shp->mask;
            /* save trap table */
            shp->st.otrapcom = 0;
            if((nsig=shp->st.trapmax*sizeof(char*))>0 || shp->st.trapcom[0])
            {
                  nsig += sizeof(char*);
                  memcpy(savsig=malloc(nsig),(char*)&shp->st.trapcom[0],nsig);
                  /* this nonsense needed for $(trap) */
                  shp->st.otrapcom = (char**)savsig;
            }
            sh_sigreset(0);
      }
      jmpval = sigsetjmp(buff.buff,0);
      if(jmpval==0)
      {
            if(comsub)
            {
                  /* disable job control */
                  sp->jobcontrol = job.jobcontrol;
                  sp->monitor = (sh_isstate(SH_MONITOR)!=0);
                  job.jobcontrol=0;
                  sh_offstate(SH_MONITOR);
                  sp->pipe = sp;
                  /* save sfstdout and status */
                  sp->saveout = sfswap(sfstdout,NIL(Sfio_t*));
                  sp->fdstatus = shp->fdstatus[1];
                  sp->tmpfd = -1;
                  sp->pipefd = -1;
                  /* use sftmp() file for standard output */
                  if(!(iop = sftmp(PIPE_BUF)))
                  {
                        sfswap(sp->saveout,sfstdout);
                        errormsg(SH_DICT,ERROR_system(1),e_tmpcreate);
                  }
                  sfswap(iop,sfstdout);
                  sfset(sfstdout,SF_READ,0);
                  shp->fdstatus[1] = IOWRITE;
            }
            else if(sp->prev)
            {
                  sp->pipe = sp->prev->pipe;
                  flags &= ~sh_state(SH_NOFORK);
            }
            sh_exec(t,flags);
      }
      if(jmpval!=SH_JMPSUB && shp->st.trapcom[0] && shp->subshell)
      {
            /* trap on EXIT not handled by child */
            char *trap=shp->st.trapcom[0];
            shp->st.trapcom[0] = 0; /* prevent recursion */
            shp->oldexit = shp->exitval;
            sh_trap(trap,0);
            free(trap);
      }
      sh_popcontext(&buff);
      if(shp->subshell==0)    /* must be child process */
      {
            subshell_data = sp->prev;
            if(jmpval==SH_JMPSCRIPT)
                  siglongjmp(*shp->jmplist,jmpval);
            sh_done(0);
      }
      if(comsub)
      {
            /* re-enable job control */
            job.jobcontrol = sp->jobcontrol;
            if(sp->monitor)
                  sh_onstate(SH_MONITOR);
            if(sp->pipefd>=0)
            {
                  /* sftmp() file has been returned into pipe */
                  iop = sh_iostream(sp->pipefd);
                  sfdisc(iop,SF_POPDISC);
                  sfclose(sfstdout);
            }
            else
            {
                  /* move tmp file to iop and restore sfstdout */
                  iop = sfswap(sfstdout,NIL(Sfio_t*));
                  if(!iop)
                  {
                        /* maybe locked try again */
                        sfclrlock(sfstdout);
                        iop = sfswap(sfstdout,NIL(Sfio_t*));
                  }
                  if(iop && sffileno(iop)==1)
                  {
                        int fd=sfsetfd(iop,3);
                        if(fd<0)
                              errormsg(SH_DICT,ERROR_system(1),e_toomany);
                        shp->sftable[fd] = iop;
                        fcntl(fd,F_SETFD,FD_CLOEXEC);
                        shp->fdstatus[fd] = (shp->fdstatus[1]|IOCLEX);
                        shp->fdstatus[1] = IOCLOSE;
                  }
                  sfset(iop,SF_READ,1);
            }
            sfswap(sp->saveout,sfstdout);
            /*  check if standard output was preserved */
            if(sp->tmpfd>=0)
            {
                  close(1);
                  fcntl(sp->tmpfd,F_DUPFD,1);
                  sh_close(sp->tmpfd);
            }
            shp->fdstatus[1] = sp->fdstatus;
      }
      if(sp->subpid)
            job_wait(sp->subpid);
      if(comsub && iop)
            sfseek(iop,(off_t)0,SEEK_SET);
      if(shp->subshell)
            shp->subshell--;
      subshell = shp->subshell;
      nv_putval(SH_SUBSHELLNOD, (char*)&subshell, NV_INT16);
#ifdef PATH_BFPATH
      path_delete((Pathcomp_t*)shp->pathlist);
      shp->pathlist = (void*)sp->pathlist;
#endif
      job_subrestore(sp->jobs);
      shp->jobenv = savecurenv;
      job.curpgid = savejobpgid;
      shp->bckpid = sp->bckpid;
      if(sp->shpwd)     /* restore environment if saved */
      {
            shp->options = sp->options;
            nv_restore(sp);
            if(sp->salias)
            {
                  shp->alias_tree = dtview(sp->salias,0);
                  table_unset(sp->salias);
                  dtclose(sp->salias);
            }
            if(sp->sfun)
            {
                  shp->fun_tree = dtview(sp->sfun,0);
                  table_unset(sp->sfun);
                  dtclose(sp->sfun);
            }
            sh_sigreset(1);
            shp->st = savst;
            shp->curenv = savecurenv;
            if(nsig)
            {
                  memcpy((char*)&shp->st.trapcom[0],savsig,nsig);
                  free((void*)savsig);
            }
            shp->options = sp->options;
            if(!shp->pwd || strcmp(sp->pwd,shp->pwd))
            {
                  /* restore PWDNOD */
                  Namval_t *pwdnod = nv_scoped(PWDNOD);
                  if(shp->pwd)
                  {
                        chdir(shp->pwd=sp->pwd);
#ifdef PATH_BFPATH
                        path_newdir(shp->pathlist);
#endif
                  }
                  if(nv_isattr(pwdnod,NV_NOFREE))
                        pwdnod->nvalue.cp = (const char*)sp->pwd;
            }
            else if(sp->shpwd != shp->pwd)
            {
                  shp->pwd = sp->pwd;
                  if(PWDNOD->nvalue.cp==sp->shpwd)
                        PWDNOD->nvalue.cp = sp->pwd;
            }
            else
                  free((void*)sp->pwd);
            if(sp->mask!=shp->mask)
                  umask(shp->mask);
      }
      subshell_data = sp->prev;
      sh_argfree(argsav,0);
      shp->trapnote = 0;
      if(shp->topfd != buff.topfd)
            sh_iorestore(buff.topfd|IOSUBSHELL,jmpval);
      if(shp->exitval > SH_EXITSIG)
      {
            int sig = shp->exitval&SH_EXITMASK;
            if(sig==SIGINT || sig== SIGQUIT)
                  sh_fault(sig);
      }
      return(iop);
}

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