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1 /* ========================================================================
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2 * Copyright 1988-2006 University of Washington
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3 *
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4 * Licensed under the Apache License, Version 2.0 (the "License");
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5 * you may not use this file except in compliance with the License.
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6 * You may obtain a copy of the License at
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7 *
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8 * http://www.apache.org/licenses/LICENSE-2.0
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9 *
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10 *
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11 * ========================================================================
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12 */
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13
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14 /*
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15 * Program: Exclusive create of a file, NFS kludge version
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16 *
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17 * Author: Mark Crispin
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18 * Networks and Distributed Computing
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19 * Computing & Communications
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20 * University of Washington
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21 * Administration Building, AG-44
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22 * Seattle, WA 98195
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23 * Internet: MRC@CAC.Washington.EDU
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24 *
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25 * Date: 17 December 1999
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26 * Last Edited: 30 August 2006
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27 */
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28
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29
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30 /* SUN-OS had an NFS, As kludgy as an albatross;
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31 * And everywhere that it was installed, It was a total loss.
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32 * -- MRC 9/25/91
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33 */
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34
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35 /* Exclusive create of a file
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36 * Accepts: file name
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37 * Return: T if success, NIL if failed, -1 if retry
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38 */
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39
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40 long crexcl (char *name)
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41 {
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42 long ret = -1;
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43 int i;
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44 char hitch[MAILTMPLEN];
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45 struct stat sb;
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46 int mask = umask (0);
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47 /* build hitching post file name */
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48 sprintf (hitch,"%s.%lu.%d.",name,(unsigned long) time (0),getpid ());
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49 i = strlen (hitch); /* append local host name */
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50 gethostname (hitch + i,(MAILTMPLEN - i) - 1);
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51 /* try to get hitching-post file */
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52 if ((i = open (hitch,O_WRONLY|O_CREAT|O_EXCL,(int) shlock_mode)) >= 0) {
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53 close (i); /* close the hitching-post */
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54 /* Note: link() may return an error even if it actually succeeded. So we
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55 * always check for success via the link count, and ignore the error if
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56 * the link count is right.
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57 */
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58 /* tie hitching-post to lock */
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59 i = link (hitch,name) ? errno : 0;
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60 /* success if link count now 2 */
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61 if (!stat (hitch,&sb) && (sb.st_nlink == 2)) ret = LONGT;
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62 else if (i == EPERM) { /* links not allowed? */
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63 /* Probably a FAT filesystem on Linux. It can't be NFS, so try creating
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64 * the lock file directly.
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65 */
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66 if ((i = open (name,O_WRONLY|O_CREAT|O_EXCL,(int) shlock_mode)) >= 0){
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67 close (i); /* close the file */
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68 ret = LONGT; /* success */
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69 }
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70 /* fail unless error is EEXIST */
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71 else if (errno != EEXIST) ret = NIL;
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72 }
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73 unlink (hitch); /* flush hitching post */
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74 }
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75 /* fail unless error is EEXIST */
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76 else if (errno != EEXIST) ret = NIL;
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77 umask (mask); /* restore previous mask */
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78 return ret;
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79 }
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