1 /* $NetBSD: timed_write.c,v 1.1.1.1 2009/06/23 10:09:01 tron Exp $ */ 2 3 /*++ 4 /* NAME 5 /* timed_write 3 6 /* SUMMARY 7 /* write operation with pre-write timeout 8 /* SYNOPSIS 9 /* #include <iostuff.h> 10 /* 11 /* ssize_t timed_write(fd, buf, len, timeout, context) 12 /* int fd; 13 /* const void *buf; 14 /* size_t len; 15 /* int timeout; 16 /* void *context; 17 /* DESCRIPTION 18 /* timed_write() performs a write() operation when the specified 19 /* descriptor becomes writable within a user-specified deadline. 20 /* 21 /* Arguments: 22 /* .IP fd 23 /* File descriptor in the range 0..FD_SETSIZE. 24 /* .IP buf 25 /* Write buffer pointer. 26 /* .IP len 27 /* Write buffer size. 28 /* .IP timeout 29 /* The deadline in seconds. If this is <= 0, the deadline feature 30 /* is disabled. 31 /* .IP context 32 /* Application context. This parameter is unused. It exists only 33 /* for the sake of VSTREAM compatibility. 34 /* DIAGNOSTICS 35 /* When the operation does not complete within the deadline, the 36 /* result value is -1, and errno is set to ETIMEDOUT. 37 /* All other returns are identical to those of a write(2) operation. 38 /* LICENSE 39 /* .ad 40 /* .fi 41 /* The Secure Mailer license must be distributed with this software. 42 /* AUTHOR(S) 43 /* Wietse Venema 44 /* IBM T.J. Watson Research 45 /* P.O. Box 704 46 /* Yorktown Heights, NY 10598, USA 47 /*--*/ 48 49 /* System library. */ 50 51 #include <sys_defs.h> 52 #include <unistd.h> 53 #include <errno.h> 54 55 /* Utility library. */ 56 57 #include <msg.h> 58 #include <iostuff.h> 59 60 /* timed_write - write with deadline */ 61 62 ssize_t timed_write(int fd, void *buf, size_t len, 63 int timeout, void *unused_context) 64 { 65 ssize_t ret; 66 67 /* 68 * Wait for a limited amount of time for something to happen. If nothing 69 * happens, report an ETIMEDOUT error. 70 * 71 * XXX Solaris 8 read() fails with EAGAIN after read-select() returns 72 * success. The code below exists just in case their write implementation 73 * is equally broken. 74 * 75 * This condition may also be found on systems where select() returns 76 * success on pipes with less than PIPE_BUF bytes of space, and with 77 * badly designed software where multiple writers are fighting for access 78 * to the same resource. 79 */ 80 for (;;) { 81 if (timeout > 0 && write_wait(fd, timeout) < 0) 82 return (-1); 83 if ((ret = write(fd, buf, len)) < 0 && timeout > 0 && errno == EAGAIN) { 84 msg_warn("write() returns EAGAIN on a writable file descriptor!"); 85 msg_warn("pausing to avoid going into a tight select/write loop!"); 86 sleep(1); 87 continue; 88 } else if (ret < 0 && errno == EINTR) { 89 continue; 90 } else { 91 return (ret); 92 } 93 } 94 } 95