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Use select() in dd(1)

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Avoid blocking in a call to splice() when no input is available.
We can now break out of dd using ^C even if the input is coming from
/dev/stdin.

Use tabs instead of spaces.
This commit is contained in:
sin 2014-06-11 12:57:10 +01:00
parent c94dfdc99d
commit 0ca8e52bc1
1 changed files with 54 additions and 40 deletions
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14
dd.c
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@ -17,6 +17,8 @@
#include <sys/ioctl.h> #include <sys/ioctl.h>
#include <sys/mount.h> #include <sys/mount.h>
#include <sys/stat.h> #include <sys/stat.h>
#include <sys/select.h>
#include <sys/time.h>
#include <sys/types.h> #include <sys/types.h>
#include <sys/vfs.h> #include <sys/vfs.h>
#include <time.h> #include <time.h>
@ -138,6 +140,8 @@ copy_splice(struct dd_config *ddc)
int ifd, ofd, p[2] = {-1, -1}; int ifd, ofd, p[2] = {-1, -1};
ssize_t r = 0; ssize_t r = 0;
size_t n = 0; size_t n = 0;
fd_set rfd, wfd;
if (prepare_copy(ddc, &ifd, &ofd) < 0) if (prepare_copy(ddc, &ifd, &ofd) < 0)
return -1; return -1;
if (pipe(p) < 0) { if (pipe(p) < 0) {
@ -156,6 +160,15 @@ copy_splice(struct dd_config *ddc)
for (;ddc->b_out != ddc->count && !sigint;) { for (;ddc->b_out != ddc->count && !sigint;) {
if (n > ddc->count - ddc->b_out) if (n > ddc->count - ddc->b_out)
n = ddc->count - ddc->b_out; n = ddc->count - ddc->b_out;
FD_ZERO(&rfd);
FD_ZERO(&wfd);
FD_SET(ifd, &rfd);
FD_SET(ofd, &wfd);
if (select(ifd > ofd ? ifd + 1 : ofd + 1, &rfd, &wfd, NULL, NULL) < 0) {
ddc->saved_errno = errno;
break;
}
if (FD_ISSET(ifd, &rfd) == 1 && FD_ISSET(ofd, &wfd) == 1) {
r = splice(ifd, NULL, p[1], NULL, n, SPLICE_F_MORE); r = splice(ifd, NULL, p[1], NULL, n, SPLICE_F_MORE);
if (r <= 0) { if (r <= 0) {
ddc->saved_errno = errno; ddc->saved_errno = errno;
@ -170,6 +183,7 @@ copy_splice(struct dd_config *ddc)
ddc->b_out += r; ddc->b_out += r;
++ddc->rec_out; ++ddc->rec_out;
} }
}
close(ifd); close(ifd);
close(ofd); close(ofd);
close(p[0]); close(p[0]);