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libbb: introduce and use nonblock_safe_read(). Yay!

Browse Source 
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
This commit is contained in:
Denis Vlasenko 2008-02-20 22:23:24 +00:00
parent ae86a338b8
commit e376d454bb
6 changed files with 75 additions and 15 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

2
include/libbb.h
View File

@ -475,6 +475,7 @@ extern void *xzalloc(size_t size);
extern void *xrealloc(void *old, size_t size);
extern ssize_t safe_read(int fd, void *buf, size_t count);
extern ssize_t nonblock_safe_read(int fd, void *buf, size_t count);
extern ssize_t full_read(int fd, void *buf, size_t count);
extern void xread(int fd, void *buf, size_t count);
extern unsigned char xread_char(int fd);
@ -482,6 +483,7 @@ extern unsigned char xread_char(int fd);
extern char *reads(int fd, char *buf, size_t count);
// Read one line a-la fgets. Reads byte-by-byte.
// Useful when it is important to not read ahead.
// Bytes are appended to pfx (which must be malloced, or NULL).
extern char *xmalloc_reads(int fd, char *pfx);
extern ssize_t read_close(int fd, void *buf, size_t count);
extern ssize_t open_read_close(const char *filename, void *buf, size_t count);

4
libbb/lineedit.c
View File

@ -1408,9 +1408,9 @@ int read_line_input(const char *prompt, char *command, int maxsize, line_input_t
parse_and_put_prompt(prompt);
while (1) {
fflush(stdout);
fflush(NULL);
if (safe_read(STDIN_FILENO, &c, 1) < 1) {
if (nonblock_safe_read(STDIN_FILENO, &c, 1) < 1) {
/* if we can't read input then exit */
goto prepare_to_die;
}

56
libbb/read.c
View File

@ -20,6 +20,58 @@ ssize_t safe_read(int fd, void *buf, size_t count)
return n;
}
/* Suppose that you are a shell. You start child processes.
* They work and eventually exit. You want to get user input.
* You read stdin. But what happens if last child switched
* its stdin into O_NONBLOCK mode?
*
* *** SURPRISE! It will affect the parent too! ***
* *** BIG SURPRISE! It stays even after child exits! ***
*
* This is a design bug in UNIX API.
* fcntl(0, F_SETFL, fcntl(0, F_GETFL, 0) | O_NONBLOCK);
* will set nonblocking mode not only on _your_ stdin, but
* also on stdin of your parent, etc.
*
* In general,
* fd2 = dup(fd1);
* fcntl(fd2, F_SETFL, fcntl(fd2, F_GETFL, 0) | O_NONBLOCK);
* sets both fd1 and fd2 to O_NONBLOCK. This includes cases
* where duping is done implicitly by fork() etc.
*
* We need
* fcntl(fd2, F_SETFD, fcntl(fd2, F_GETFD, 0) | O_NONBLOCK);
* (note SETFD, not SETFL!) but such thing doesn't exist.
*
* Alternatively, we need nonblocking_read(fd, ...) which doesn't
* require O_NONBLOCK dance at all. Actually, it exists:
* n = recv(fd, buf, len, MSG_DONTWAIT);
* "MSG_DONTWAIT:
* Enables non-blocking operation; if the operation
* would block, EAGAIN is returned."
* but recv() works only for sockets!
*
* So far I don't see any good solution, I can only propose
* that affected readers should be careful and use this routine,
* which detects EAGAIN and uses poll() to wait on the fd.
* Thanksfully, poll() doesn't give rat's ass about O_NONBLOCK flag.
*/
ssize_t nonblock_safe_read(int fd, void *buf, size_t count)
{
struct pollfd pfd[1];
ssize_t n;
while (1) {
n = safe_read(fd, buf, count);
if (n >= 0 || errno != EAGAIN)
return n;
/* fd is in O_NONBLOCK mode. Wait using poll and repeat */
pfd[0].fd = fd;
pfd[0].events = POLLIN;
safe_poll(pfd, 1, -1);
}
}
/*
* Read all of the supplied buffer from a file.
* This does multiple reads as necessary.
@ -93,6 +145,7 @@ char *reads(int fd, char *buffer, size_t size)
// Read one line a-la fgets. Reads byte-by-byte.
// Useful when it is important to not read ahead.
// Bytes are appended to pfx (which must be malloced, or NULL).
char *xmalloc_reads(int fd, char *buf)
{
char *p;
@ -106,7 +159,8 @@ char *xmalloc_reads(int fd, char *buf)
p = buf + sz;
sz += 128;
}
if (safe_read(fd, p, 1) != 1) { /* EOF/error */
/* nonblock_safe_read() because we are used by e.g. shells */
if (nonblock_safe_read(fd, p, 1) != 1) { /* EOF/error */
if (p == buf) {
/* we read nothing [and buf was NULL initially] */
free(buf);

11
shell/ash.c
View File

@ -5428,7 +5428,7 @@ expbackq(union node *cmd, int quoted, int quotes)
read:
if (in.fd < 0)
break;
i = safe_read(in.fd, buf, sizeof(buf));
i = nonblock_safe_read(in.fd, buf, sizeof(buf));
TRACE(("expbackq: read returns %d\n", i));
if (i <= 0)
break;
@ -8678,7 +8678,7 @@ preadfd(void)
retry:
#if ENABLE_FEATURE_EDITING
if (!iflag || parsefile->fd)
nr = safe_read(parsefile->fd, buf, BUFSIZ - 1);
nr = nonblock_safe_read(parsefile->fd, buf, BUFSIZ - 1);
else {
#if ENABLE_FEATURE_TAB_COMPLETION
line_input_state->path_lookup = pathval();
@ -8700,9 +8700,11 @@ preadfd(void)
}
}
#else
nr = safe_read(parsefile->fd, buf, BUFSIZ - 1);
nr = nonblock_safe_read(parsefile->fd, buf, BUFSIZ - 1);
#endif
#if 0
/* nonblock_safe_read() handles this problem */
if (nr < 0) {
if (parsefile->fd == 0 && errno == EWOULDBLOCK) {
int flags = fcntl(0, F_GETFL);
@ -8715,6 +8717,7 @@ preadfd(void)
}
}
}
#endif
return nr;
}
@ -11801,7 +11804,7 @@ readcmd(int argc, char **argv)
backslash = 0;
STARTSTACKSTR(p);
do {
if (read(0, &c, 1) != 1) {
if (nonblock_safe_read(0, &c, 1) != 1) {
status = 1;
break;
}

8
shell/hush.c
View File

@ -1273,10 +1273,10 @@ static void get_user_input(struct in_str *i)
prompt_str = setup_prompt_string(i->promptmode);
#if ENABLE_FEATURE_EDITING
/* Enable command line editing only while a command line
* is actually being read; otherwise, we'll end up bequeathing
* atexit() handlers and other unwanted stuff to our
* child processes (rob@sysgo.de) */
r = read_line_input(prompt_str, user_input_buf, BUFSIZ-1, line_input_state);
* is actually being read */
do {
r = read_line_input(prompt_str, user_input_buf, BUFSIZ-1, line_input_state);
} while (r == 0); /* repeat if Ctrl-C */
i->eof_flag = (r < 0);
if (i->eof_flag) { /* EOF/error detected */
user_input_buf[0] = EOF; /* yes, it will be truncated, it's ok */

9
shell/msh.c
View File

@ -42,6 +42,7 @@
# define xmalloc(size) malloc(size)
# define msh_main(argc,argv) main(argc,argv)
# define safe_read(fd,buf,count) read(fd,buf,count)
# define nonblock_safe_read(fd,buf,count) read(fd,buf,count)
# define NOT_LONE_DASH(s) ((s)[0] != '-' || (s)[1])
# define LONE_CHAR(s,c) ((s)[0] == (c) && !(s)[1])
# define ATTRIBUTE_NORETURN __attribute__ ((__noreturn__))
@ -3376,7 +3377,7 @@ static int doread(struct op *t)
}
for (wp = t->words + 1; *wp; wp++) {
for (cp = global_env.linep; !nl && cp < elinep - 1; cp++) {
nb = read(0, cp, sizeof(*cp));
nb = nonblock_safe_read(0, cp, sizeof(*cp));
if (nb != sizeof(*cp))
break;
nl = (*cp == '\n');
@ -4799,7 +4800,7 @@ static int filechar(struct ioarg *ap)
if (i)
lseek(ap->afile, ap->afpos, SEEK_SET);
i = safe_read(ap->afile, bp->buf, sizeof(bp->buf));
i = nonblock_safe_read(ap->afile, bp->buf, sizeof(bp->buf));
if (i <= 0) {
closef(ap->afile);
return 0;
@ -4830,7 +4831,7 @@ static int filechar(struct ioarg *ap)
return c;
}
#endif
i = safe_read(ap->afile, &c, sizeof(c));
i = nonblock_safe_read(ap->afile, &c, sizeof(c));
return i == sizeof(c) ? (c & 0x7f) : (closef(ap->afile), 0);
}
@ -4841,7 +4842,7 @@ static int herechar(struct ioarg *ap)
{
char c;
if (read(ap->afile, &c, sizeof(c)) != sizeof(c)) {
if (nonblock_safe_read(ap->afile, &c, sizeof(c)) != sizeof(c)) {
close(ap->afile);
c = '\0';
}