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by Joakim Tjernlund <Joakim.Tjernlund AT transmode.se> function old new delta xmalloc_open_read_close 190 181 -9
294 lines
6.8 KiB
C
294 lines
6.8 KiB
C
/* vi: set sw=4 ts=4: */
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/*
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* Utility routines.
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*
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* Copyright (C) 1999-2004 by Erik Andersen <andersen@codepoet.org>
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*
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* Licensed under GPLv2 or later, see file LICENSE in this tarball for details.
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*/
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#include "libbb.h"
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ssize_t safe_read(int fd, void *buf, size_t count)
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{
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ssize_t n;
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do {
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n = read(fd, buf, count);
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} while (n < 0 && errno == EINTR);
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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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* Thankfully, poll() doesn't care 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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* Returns the amount read, or -1 on an error.
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* A short read is returned on an end of file.
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*/
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ssize_t full_read(int fd, void *buf, size_t len)
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{
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ssize_t cc;
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ssize_t total;
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total = 0;
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while (len) {
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cc = safe_read(fd, buf, len);
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if (cc < 0) {
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if (total) {
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/* we already have some! */
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/* user can do another read to know the error code */
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return total;
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}
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return cc; /* read() returns -1 on failure. */
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}
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if (cc == 0)
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break;
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buf = ((char *)buf) + cc;
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total += cc;
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len -= cc;
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}
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return total;
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}
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// Die with an error message if we can't read the entire buffer.
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void xread(int fd, void *buf, size_t count)
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{
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if (count) {
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ssize_t size = full_read(fd, buf, count);
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if (size != count)
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bb_error_msg_and_die("short read");
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}
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}
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// Die with an error message if we can't read one character.
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unsigned char xread_char(int fd)
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{
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char tmp;
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xread(fd, &tmp, 1);
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return tmp;
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}
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// Read one line a-la fgets. Works only on seekable streams
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char *reads(int fd, char *buffer, size_t size)
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{
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char *p;
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if (size < 2)
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return NULL;
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size = full_read(fd, buffer, size-1);
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if ((ssize_t)size <= 0)
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return NULL;
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buffer[size] = '\0';
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p = strchr(buffer, '\n');
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if (p) {
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off_t offset;
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*p++ = '\0';
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// avoid incorrect (unsigned) widening
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offset = (off_t)(p - buffer) - (off_t)size;
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// set fd position right after '\n'
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if (offset && lseek(fd, offset, SEEK_CUR) == (off_t)-1)
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return NULL;
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}
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return buffer;
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}
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// Reads one line a-la fgets (but doesn't save terminating '\n').
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// Reads byte-by-byte. 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, size_t *maxsz_p)
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{
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char *p;
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size_t sz = buf ? strlen(buf) : 0;
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size_t maxsz = maxsz_p ? *maxsz_p : MAXINT(size_t);
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goto jump_in;
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while (sz < maxsz) {
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if (p - buf == sz) {
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jump_in:
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buf = xrealloc(buf, sz + 128);
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p = buf + sz;
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sz += 128;
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}
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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) { /* we read nothing */
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free(buf);
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return NULL;
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}
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break;
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}
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if (*p == '\n')
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break;
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p++;
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}
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*p = '\0';
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if (maxsz_p)
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*maxsz_p = p - buf;
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p++;
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return xrealloc(buf, p - buf);
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}
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ssize_t read_close(int fd, void *buf, size_t size)
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{
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/*int e;*/
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size = full_read(fd, buf, size);
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/*e = errno;*/
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close(fd);
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/*errno = e;*/
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return size;
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}
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ssize_t open_read_close(const char *filename, void *buf, size_t size)
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{
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int fd = open(filename, O_RDONLY);
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if (fd < 0)
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return fd;
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return read_close(fd, buf, size);
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}
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// Read (potentially big) files in one go. File size is estimated by
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// lseek to end.
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void *xmalloc_open_read_close(const char *filename, size_t *sizep)
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{
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char *buf;
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size_t size;
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int fd;
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off_t len;
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struct stat st;
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fd = open(filename, O_RDONLY);
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if (fd < 0)
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return NULL;
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st.st_size = 0; /* in case fstat fail, define to 0 */
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fstat(fd, &st);
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/* /proc/N/stat files report len 0 here */
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/* In order to make such files readable, we add small const */
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len = st.st_size | 0x3ff; /* read only 1k on unseekable files */
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size = sizep ? *sizep : INT_MAX;
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if (len < size)
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size = len;
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buf = xmalloc(size + 1);
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size = read_close(fd, buf, size);
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if ((ssize_t)size < 0) {
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free(buf);
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return NULL;
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}
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xrealloc(buf, size + 1);
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buf[size] = '\0';
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if (sizep)
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*sizep = size;
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return buf;
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}
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#ifdef USING_LSEEK_TO_GET_SIZE
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/* Alternatively, file size can be obtained by lseek to the end.
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* The code is slightly bigger. Retained in case fstat approach
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* will not work for some weird cases (/proc, block devices, etc).
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* (NB: lseek also can fail to work for some weird files) */
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// Read (potentially big) files in one go. File size is estimated by
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// lseek to end.
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void *xmalloc_open_read_close(const char *filename, size_t *sizep)
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{
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char *buf;
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size_t size;
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int fd;
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off_t len;
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fd = open(filename, O_RDONLY);
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if (fd < 0)
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return NULL;
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/* /proc/N/stat files report len 0 here */
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/* In order to make such files readable, we add small const */
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size = 0x3ff; /* read only 1k on unseekable files */
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len = lseek(fd, 0, SEEK_END) | 0x3ff; /* + up to 1k */
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if (len != (off_t)-1) {
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xlseek(fd, 0, SEEK_SET);
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size = sizep ? *sizep : INT_MAX;
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if (len < size)
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size = len;
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}
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buf = xmalloc(size + 1);
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size = read_close(fd, buf, size);
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if ((ssize_t)size < 0) {
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free(buf);
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return NULL;
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}
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xrealloc(buf, size + 1);
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buf[size] = '\0';
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if (sizep)
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*sizep = size;
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return buf;
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}
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#endif
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void *xmalloc_xopen_read_close(const char *filename, size_t *sizep)
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{
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void *buf = xmalloc_open_read_close(filename, sizep);
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if (!buf)
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bb_perror_msg_and_die("can't read '%s'", filename);
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return buf;
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}
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