1 | /* |
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2 | * Set or clear file descriptor flags. |
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3 | * |
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4 | * Simple functions (wrappers around fcntl) to set or clear file descriptor |
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5 | * flags like close-on-exec or nonblocking I/O. |
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6 | * |
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7 | * Copyright 2008 Board of Trustees, Leland Stanford Jr. University |
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8 | * Copyright (c) 2004, 2005, 2006 |
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9 | * by Internet Systems Consortium, Inc. ("ISC") |
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10 | * Copyright (c) 1991, 1994, 1995, 1996, 1997, 1998, 1999, 2000, 2001, |
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11 | * 2002, 2003 by The Internet Software Consortium and Rich Salz |
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12 | * |
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13 | * See LICENSE for licensing terms. |
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14 | */ |
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15 | |
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16 | #include <config.h> |
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17 | #include <portable/system.h> |
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18 | |
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19 | #include <errno.h> |
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20 | #include <fcntl.h> |
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21 | #ifndef O_NONBLOCK |
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22 | # include <sys/ioctl.h> |
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23 | # if HAVE_SYS_FILIO_H |
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24 | # include <sys/filio.h> |
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25 | # endif |
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26 | #endif |
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27 | |
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28 | #include <util/util.h> |
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29 | |
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30 | |
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31 | /* |
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32 | * Set a file to close-on-exec (or clear that setting if the flag is false), |
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33 | * returning true on success and false on failure. |
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34 | * |
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35 | * One is supposed to retrieve the flags, add FD_CLOEXEC, and then set them, |
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36 | * although I've never seen a system with any flags other than close-on-exec. |
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37 | * Do it right anyway; it's not that expensive. |
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38 | */ |
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39 | bool |
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40 | fdflag_close_exec(int fd, bool flag) |
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41 | { |
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42 | int oflag, mode; |
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43 | |
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44 | oflag = fcntl(fd, F_GETFD, 0); |
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45 | if (oflag < 0) |
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46 | return false; |
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47 | mode = flag ? (oflag | FD_CLOEXEC) : (oflag & ~FD_CLOEXEC); |
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48 | return (fcntl(fd, F_SETFD, mode) == 0); |
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49 | } |
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50 | |
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51 | |
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52 | /* |
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53 | * Set a file descriptor to nonblocking (or clear the nonblocking flag if flag |
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54 | * is false), returning true on success and false on failure. |
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55 | * |
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56 | * Always use O_NONBLOCK; O_NDELAY is not the same thing historically. The |
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57 | * semantics of O_NDELAY are that if the read would block, it returns 0 |
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58 | * instead. This is indistinguishable from an end of file condition. POSIX |
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59 | * added O_NONBLOCK, which requires read to return -1 and set errno to EAGAIN, |
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60 | * which is what we want. |
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61 | * |
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62 | * FNDELAY (4.3BSD) originally did the correct thing, although it has a |
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63 | * different incompatibility (affecting all users of a socket rather than just |
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64 | * a file descriptor and returning EWOULDBLOCK instead of EAGAIN) that we |
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65 | * probably don't care about. Using it is probably safe, but BSD should also |
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66 | * have the ioctl, and at least on Solaris FNDELAY does the same thing as |
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67 | * O_NDELAY, not O_NONBLOCK. So if we don't have O_NONBLOCK, fall back to the |
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68 | * ioctl instead. |
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69 | * |
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70 | * Reference: Stevens, Advanced Unix Programming, pg. 364. |
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71 | * |
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72 | * Note that O_NONBLOCK is known not to work on earlier versions of ULTRIX, |
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73 | * SunOS, and AIX, possibly not setting the socket nonblocking at all, despite |
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74 | * the fact that they do define it. It works in later SunOS and, current AIX, |
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75 | * however, and a 1999-10-25 survey of current operating systems failed to |
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76 | * turn up any that didn't handle it correctly (as required by POSIX), while |
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77 | * HP-UX 11.00 did use the broken return-zero semantics of O_NDELAY (most |
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78 | * other operating systems surveyed treated O_NDELAY as synonymous with |
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79 | * O_NONBLOCK). Accordingly, we currently unconditionally use O_NONBLOCK. If |
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80 | * this causes too many problems, an autoconf test may be required. |
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81 | */ |
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82 | #ifdef O_NONBLOCK |
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83 | bool |
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84 | fdflag_nonblocking(int fd, bool flag) |
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85 | { |
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86 | int mode; |
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87 | |
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88 | mode = fcntl(fd, F_GETFL, 0); |
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89 | if (mode < 0) |
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90 | return false; |
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91 | mode = (flag ? (mode | O_NONBLOCK) : (mode & ~O_NONBLOCK)); |
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92 | return (fcntl(fd, F_SETFL, mode) == 0); |
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93 | } |
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94 | #else /* !O_NONBLOCK */ |
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95 | int |
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96 | nonblocking(int fd, bool flag) |
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97 | { |
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98 | int state; |
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99 | |
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100 | state = flag ? 1 : 0; |
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101 | return ioctl(fd, FIONBIO, &state); |
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102 | } |
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103 | #endif /* !O_NONBLOCK */ |
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