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libbb: introduce and use nonblock_safe_read(). Yay!
Our shells are immune from this nasty O_NONBLOCK now! function old new delta nonblock_safe_read - 78 +78 file_get 276 295 +19 generateMTFValues 428 435 +7 read_line_input 1776 1772 -4 preadbuffer 543 450 -93 ------------------------------------------------------------------------------ (add/remove: 1/0 grow/shrink: 2/2 up/down: 104/-97) Total: 7 bytes text data bss dec hex filename 615190 715 23924 639829 9c355 busybox_old 615168 715 23924 639807 9c33f busybox_unstripped
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e376d454bb
@ -475,6 +475,7 @@ extern void *xzalloc(size_t size);
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extern void *xrealloc(void *old, size_t size);
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extern ssize_t safe_read(int fd, void *buf, size_t count);
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extern ssize_t nonblock_safe_read(int fd, void *buf, size_t count);
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extern ssize_t full_read(int fd, void *buf, size_t count);
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extern void xread(int fd, void *buf, size_t count);
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extern unsigned char xread_char(int fd);
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@ -482,6 +483,7 @@ extern unsigned char xread_char(int fd);
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extern char *reads(int fd, char *buf, size_t count);
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// Read one line a-la fgets. Reads byte-by-byte.
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// Useful when it is important to not read ahead.
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// Bytes are appended to pfx (which must be malloced, or NULL).
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extern char *xmalloc_reads(int fd, char *pfx);
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extern ssize_t read_close(int fd, void *buf, size_t count);
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extern ssize_t open_read_close(const char *filename, void *buf, size_t count);
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@ -1408,9 +1408,9 @@ int read_line_input(const char *prompt, char *command, int maxsize, line_input_t
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parse_and_put_prompt(prompt);
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while (1) {
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fflush(stdout);
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fflush(NULL);
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if (safe_read(STDIN_FILENO, &c, 1) < 1) {
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if (nonblock_safe_read(STDIN_FILENO, &c, 1) < 1) {
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/* if we can't read input then exit */
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goto prepare_to_die;
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}
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56
libbb/read.c
56
libbb/read.c
@ -20,6 +20,58 @@ ssize_t safe_read(int fd, void *buf, size_t count)
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return n;
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}
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/* Suppose that you are a shell. You start child processes.
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* They work and eventually exit. You want to get user input.
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* You read stdin. But what happens if last child switched
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* its stdin into O_NONBLOCK mode?
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*
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* *** SURPRISE! It will affect the parent too! ***
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* *** BIG SURPRISE! It stays even after child exits! ***
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*
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* This is a design bug in UNIX API.
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* fcntl(0, F_SETFL, fcntl(0, F_GETFL, 0) | O_NONBLOCK);
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* will set nonblocking mode not only on _your_ stdin, but
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* also on stdin of your parent, etc.
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*
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* In general,
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* fd2 = dup(fd1);
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* fcntl(fd2, F_SETFL, fcntl(fd2, F_GETFL, 0) | O_NONBLOCK);
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* sets both fd1 and fd2 to O_NONBLOCK. This includes cases
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* where duping is done implicitly by fork() etc.
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*
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* We need
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* fcntl(fd2, F_SETFD, fcntl(fd2, F_GETFD, 0) | O_NONBLOCK);
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* (note SETFD, not SETFL!) but such thing doesn't exist.
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*
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* Alternatively, we need nonblocking_read(fd, ...) which doesn't
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* require O_NONBLOCK dance at all. Actually, it exists:
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* n = recv(fd, buf, len, MSG_DONTWAIT);
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* "MSG_DONTWAIT:
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* Enables non-blocking operation; if the operation
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* would block, EAGAIN is returned."
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* but recv() works only for sockets!
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*
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* So far I don't see any good solution, I can only propose
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* that affected readers should be careful and use this routine,
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* which detects EAGAIN and uses poll() to wait on the fd.
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* Thanksfully, poll() doesn't give rat's ass about O_NONBLOCK flag.
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*/
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ssize_t nonblock_safe_read(int fd, void *buf, size_t count)
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{
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struct pollfd pfd[1];
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ssize_t n;
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while (1) {
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n = safe_read(fd, buf, count);
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if (n >= 0 || errno != EAGAIN)
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return n;
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/* fd is in O_NONBLOCK mode. Wait using poll and repeat */
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pfd[0].fd = fd;
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pfd[0].events = POLLIN;
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safe_poll(pfd, 1, -1);
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}
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}
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/*
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* Read all of the supplied buffer from a file.
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* This does multiple reads as necessary.
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@ -93,6 +145,7 @@ char *reads(int fd, char *buffer, size_t size)
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// Read one line a-la fgets. Reads byte-by-byte.
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// Useful when it is important to not read ahead.
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// Bytes are appended to pfx (which must be malloced, or NULL).
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char *xmalloc_reads(int fd, char *buf)
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{
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char *p;
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@ -106,7 +159,8 @@ char *xmalloc_reads(int fd, char *buf)
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p = buf + sz;
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sz += 128;
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}
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if (safe_read(fd, p, 1) != 1) { /* EOF/error */
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/* nonblock_safe_read() because we are used by e.g. shells */
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if (nonblock_safe_read(fd, p, 1) != 1) { /* EOF/error */
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if (p == buf) {
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/* we read nothing [and buf was NULL initially] */
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free(buf);
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11
shell/ash.c
11
shell/ash.c
@ -5428,7 +5428,7 @@ expbackq(union node *cmd, int quoted, int quotes)
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read:
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if (in.fd < 0)
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break;
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i = safe_read(in.fd, buf, sizeof(buf));
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i = nonblock_safe_read(in.fd, buf, sizeof(buf));
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TRACE(("expbackq: read returns %d\n", i));
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if (i <= 0)
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break;
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@ -8678,7 +8678,7 @@ preadfd(void)
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retry:
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#if ENABLE_FEATURE_EDITING
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if (!iflag || parsefile->fd)
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nr = safe_read(parsefile->fd, buf, BUFSIZ - 1);
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nr = nonblock_safe_read(parsefile->fd, buf, BUFSIZ - 1);
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else {
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#if ENABLE_FEATURE_TAB_COMPLETION
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line_input_state->path_lookup = pathval();
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@ -8700,9 +8700,11 @@ preadfd(void)
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}
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}
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#else
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nr = safe_read(parsefile->fd, buf, BUFSIZ - 1);
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nr = nonblock_safe_read(parsefile->fd, buf, BUFSIZ - 1);
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#endif
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#if 0
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/* nonblock_safe_read() handles this problem */
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if (nr < 0) {
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if (parsefile->fd == 0 && errno == EWOULDBLOCK) {
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int flags = fcntl(0, F_GETFL);
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@ -8715,6 +8717,7 @@ preadfd(void)
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}
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}
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}
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#endif
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return nr;
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}
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@ -11801,7 +11804,7 @@ readcmd(int argc, char **argv)
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backslash = 0;
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STARTSTACKSTR(p);
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do {
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if (read(0, &c, 1) != 1) {
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if (nonblock_safe_read(0, &c, 1) != 1) {
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status = 1;
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break;
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}
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@ -1273,10 +1273,10 @@ static void get_user_input(struct in_str *i)
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prompt_str = setup_prompt_string(i->promptmode);
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#if ENABLE_FEATURE_EDITING
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/* Enable command line editing only while a command line
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* is actually being read; otherwise, we'll end up bequeathing
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* atexit() handlers and other unwanted stuff to our
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* child processes (rob@sysgo.de) */
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r = read_line_input(prompt_str, user_input_buf, BUFSIZ-1, line_input_state);
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* is actually being read */
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do {
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r = read_line_input(prompt_str, user_input_buf, BUFSIZ-1, line_input_state);
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} while (r == 0); /* repeat if Ctrl-C */
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i->eof_flag = (r < 0);
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if (i->eof_flag) { /* EOF/error detected */
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user_input_buf[0] = EOF; /* yes, it will be truncated, it's ok */
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@ -42,6 +42,7 @@
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# define xmalloc(size) malloc(size)
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# define msh_main(argc,argv) main(argc,argv)
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# define safe_read(fd,buf,count) read(fd,buf,count)
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# define nonblock_safe_read(fd,buf,count) read(fd,buf,count)
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# define NOT_LONE_DASH(s) ((s)[0] != '-' || (s)[1])
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# define LONE_CHAR(s,c) ((s)[0] == (c) && !(s)[1])
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# define ATTRIBUTE_NORETURN __attribute__ ((__noreturn__))
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@ -3376,7 +3377,7 @@ static int doread(struct op *t)
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}
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for (wp = t->words + 1; *wp; wp++) {
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for (cp = global_env.linep; !nl && cp < elinep - 1; cp++) {
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nb = read(0, cp, sizeof(*cp));
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nb = nonblock_safe_read(0, cp, sizeof(*cp));
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if (nb != sizeof(*cp))
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break;
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nl = (*cp == '\n');
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@ -4799,7 +4800,7 @@ static int filechar(struct ioarg *ap)
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if (i)
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lseek(ap->afile, ap->afpos, SEEK_SET);
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i = safe_read(ap->afile, bp->buf, sizeof(bp->buf));
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i = nonblock_safe_read(ap->afile, bp->buf, sizeof(bp->buf));
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if (i <= 0) {
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closef(ap->afile);
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return 0;
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@ -4830,7 +4831,7 @@ static int filechar(struct ioarg *ap)
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return c;
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}
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#endif
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i = safe_read(ap->afile, &c, sizeof(c));
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i = nonblock_safe_read(ap->afile, &c, sizeof(c));
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return i == sizeof(c) ? (c & 0x7f) : (closef(ap->afile), 0);
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}
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@ -4841,7 +4842,7 @@ static int herechar(struct ioarg *ap)
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{
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char c;
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if (read(ap->afile, &c, sizeof(c)) != sizeof(c)) {
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if (nonblock_safe_read(ap->afile, &c, sizeof(c)) != sizeof(c)) {
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close(ap->afile);
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c = '\0';
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}
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