busybox/libbb/read_printf.c

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/* vi: set sw=4 ts=4: */
/*
* Utility routines.
*
* Copyright (C) 1999-2004 by Erik Andersen <andersen@codepoet.org>
*
* Licensed under GPLv2 or later, see file LICENSE in this source tree.
*/
#include "libbb.h"
/* 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) | 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) | 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) | 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.
* Thankfully, poll() doesn't care about O_NONBLOCK flag.
*/
ssize_t FAST_FUNC nonblock_immune_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;
/* note: safe_poll pulls in printf */
safe_poll(pfd, 1, -1);
}
}
// Reads one line a-la fgets (but doesn't save terminating '\n').
// 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* FAST_FUNC xmalloc_reads(int fd, size_t *maxsz_p)
{
char *p;
char *buf = NULL;
size_t sz = 0;
size_t maxsz = maxsz_p ? *maxsz_p : (INT_MAX - 4095);
goto jump_in;
while (sz < maxsz) {
if ((size_t)(p - buf) == sz) {
jump_in:
buf = xrealloc(buf, sz + 128);
p = buf + sz;
sz += 128;
}
if (nonblock_immune_read(fd, p, 1) != 1) {
/* EOF/error */
if (p == buf) { /* we read nothing */
free(buf);
return NULL;
}
break;
}
if (*p == '\n')
break;
p++;
}
*p = '\0';
if (maxsz_p)
*maxsz_p = p - buf;
p++;
return xrealloc(buf, p - buf);
}
// Read (potentially big) files in one go. File size is estimated
// by stat. Extra '\0' byte is appended.
void* FAST_FUNC xmalloc_read(int fd, size_t *maxsz_p)
{
char *buf;
size_t size, rd_size, total;
size_t to_read;
struct stat st;
to_read = maxsz_p ? *maxsz_p : (INT_MAX - 4095); /* max to read */
/* Estimate file size */
st.st_size = 0; /* in case fstat fails, assume 0 */
fstat(fd, &st);
/* /proc/N/stat files report st_size 0 */
/* In order to make such files readable, we add small const */
size = (st.st_size | 0x3ff) + 1;
total = 0;
buf = NULL;
while (1) {
if (to_read < size)
size = to_read;
buf = xrealloc(buf, total + size + 1);
rd_size = full_read(fd, buf + total, size);
if ((ssize_t)rd_size == (ssize_t)(-1)) { /* error */
free(buf);
return NULL;
}
total += rd_size;
if (rd_size < size) /* EOF */
break;
if (to_read <= rd_size)
break;
to_read -= rd_size;
/* grow by 1/8, but in [1k..64k] bounds */
size = ((total / 8) | 0x3ff) + 1;
if (size > 64*1024)
size = 64*1024;
}
buf = xrealloc(buf, total + 1);
buf[total] = '\0';
if (maxsz_p)
*maxsz_p = total;
return buf;
}
#ifdef USING_LSEEK_TO_GET_SIZE
/* Alternatively, file size can be obtained by lseek to the end.
* The code is slightly bigger. Retained in case fstat approach
* will not work for some weird cases (/proc, block devices, etc).
* (NB: lseek also can fail to work for some weird files) */
// Read (potentially big) files in one go. File size is estimated by
// lseek to end.
void* FAST_FUNC xmalloc_open_read_close(const char *filename, size_t *maxsz_p)
{
char *buf;
size_t size;
int fd;
off_t len;
fd = open(filename, O_RDONLY);
if (fd < 0)
return NULL;
/* /proc/N/stat files report len 0 here */
/* In order to make such files readable, we add small const */
size = 0x3ff; /* read only 1k on unseekable files */
len = lseek(fd, 0, SEEK_END) | 0x3ff; /* + up to 1k */
if (len != (off_t)-1) {
xlseek(fd, 0, SEEK_SET);
size = maxsz_p ? *maxsz_p : (INT_MAX - 4095);
if (len < size)
size = len;
}
buf = xmalloc(size + 1);
size = read_close(fd, buf, size);
if ((ssize_t)size < 0) {
free(buf);
return NULL;
}
buf = xrealloc(buf, size + 1);
buf[size] = '\0';
if (maxsz_p)
*maxsz_p = size;
return buf;
}
#endif
// Read (potentially big) files in one go. File size is estimated
// by stat.
void* FAST_FUNC xmalloc_open_read_close(const char *filename, size_t *maxsz_p)
{
char *buf;
int fd;
fd = open(filename, O_RDONLY);
if (fd < 0)
return NULL;
buf = xmalloc_read(fd, maxsz_p);
close(fd);
return buf;
}
/* Die with an error message if we can't read the entire buffer. */
void FAST_FUNC xread(int fd, void *buf, size_t count)
{
if (count) {
ssize_t size = full_read(fd, buf, count);
if ((size_t)size != count)
bb_error_msg_and_die("short read");
}
}
/* Die with an error message if we can't read one character. */
unsigned char FAST_FUNC xread_char(int fd)
{
char tmp;
xread(fd, &tmp, 1);
return tmp;
}
void* FAST_FUNC xmalloc_xopen_read_close(const char *filename, size_t *maxsz_p)
{
void *buf = xmalloc_open_read_close(filename, maxsz_p);
if (!buf)
bb_perror_msg_and_die("can't read '%s'", filename);
return buf;
}