[EMAIL PROTECTED] wrote: > From fd13986de32af31621b1badbcf7bfb5626648e0e Mon Sep 17 00:00:00 2001 > From: Sukadev Bhattiprolu <[EMAIL PROTECTED]> > Date: Mon, 16 Jun 2008 18:41:05 -0700 > Subject: [PATCH] Save/restore state of unnamed pipes > > Design: > > Current Linux kernels provide ability to read/write contents of FIFOs > using /proc. i.e 'cat /proc/pid/fd/read-side-fd' prints the unread data > in the FIFO. Similarly, 'cat foo > /proc/pid/fd/read-sid-fd' appends > the contents of 'foo' to the unread contents of the FIFO. > > So to save/restore the state of the pipe, a simple implementation is > to read the from the unnamed pipe's fd and save to the checkpoint-file. > When restoring, create a pipe (using PT_PIPE()) in the child process, > read the contents of the pipe from the checkpoint file and write it to > the newly created pipe. > > Its fairly straightforward, except for couple of notes: > > - when we read contents of '/proc/pid/fd/read-side-fd' we drain > the pipe such that when the checkpointed application resumes, > it will not find any data. To fix this, we read from the > 'read-side-fd' and write it back to the 'read-side-fd' in > addition to writing to the checkpoint file.
One issue with this approach is that the operation (checkpoint) becomes non-transparent to the "checkpointee"s: re-writing the data back into the pipe/fifo may generate a SIGIO at the read-side of the pipe/fifo, or an inotify event on the inode, without a real reason. This may confuse the application if its logic relies on "normal" behavior. > > - there does not seem to be a mechanism to determine the count > of unread bytes in the file. Current implmentation assumes a > maximum of 64K bytes (PIPE_BUFS * PAGE_SIZE on i386) and fails > if the pipe is not fully drained. > > Basic unit-testing done at this point (using tests/pipe.c). > > TODO: > - Additional testing (with multiple-processes and multiple-pipes) > - Named-pipes > > Signed-off-by: Sukadev Bhattiprolu <[EMAIL PROTECTED]> > --- > cr.c | 215 > ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++---- > 1 files changed, 203 insertions(+), 12 deletions(-) > > diff --git a/cr.c b/cr.c > index 5163a3d..0cb9774 100644 > --- a/cr.c > +++ b/cr.c > @@ -84,6 +84,11 @@ typedef struct fdinfo_t { > char name[128]; /* file name. NULL if anonymous (pipe, > socketpair) */ > } fdinfo_t; > > +typedef struct fifoinfo_t { > + int fi_fd; /* fifo's read-side fd */ > + int fi_length; /* number of bytes in the fifo */ > +} fifofdinfo_t; > + > typedef struct memseg_t { > unsigned long start; /* memory segment start address */ > unsigned long end; /* memory segment end address */ > @@ -468,6 +473,128 @@ out: > return rc; > } > > +static int estimate_fifo_unread_bytes(pinfo_t *pi, int fd) > +{ > + /* > + * Is there a way to find the number of bytes remaining to be > + * read in a fifo ? If not, can we print it in fdinfo ? > + * > + * Return 64K (PIPE_BUFS * PAGE_SIZE) for now. > + */ > + return 65536; > +} > + > +static void ensure_fifo_has_drained(char *fname, int fifo_fd) > +{ > + int rc, c; > + > + rc = read(fifo_fd, &c, 1); > + if (rc != -1 && errno != EAGAIN) { > + ERROR("FIFO '%s' not drained fully. rc %d, c %d " > + "errno %d\n", fname, rc, c, errno); > + } > + > +} > + > +static int save_process_fifo_info(pinfo_t *pi, int fd) > +{ > + int i; > + int rc; > + int nbytes; > + int fifo_fd; > + int pbuf_size; > + pid_t pid = pi->pid; > + char fname[256]; > + fdinfo_t *fi = pi->fi; > + char *pbuf; > + fifofdinfo_t fifofdinfo; > + > + write_item(fd, "FIFO", NULL, 0); > + > + for (i = 0; i < pi->nf; i++) { > + if (! S_ISFIFO(fi[i].mode)) > + continue; > + > + DEBUG("FIFO fd %d (%s), flag 0x%x\n", fi[i].fdnum, fi[i].name, > + fi[i].flag); > + > + if (!(fi[i].flag & O_WRONLY)) > + continue; > + > + pbuf_size = estimate_fifo_unread_bytes(pi, fd); > + > + pbuf = (char *)malloc(pbuf_size); > + if (!pbuf) { > + ERROR("Unable to allocate FIFO buffer of size %d\n", > + pbuf_size); > + } > + memset(pbuf, 0, pbuf_size); > + > + sprintf(fname, "/proc/%u/fd/%u", pid, fi[i].fdnum); > + > + /* > + * Open O_NONBLOCK so read does not block if fifo has fewer > + * bytes than our estimate. > + */ > + fifo_fd = open(fname, O_RDWR|O_NONBLOCK); > + if (fifo_fd < 0) > + ERROR("Error %d opening FIFO '%s'\n", errno, fname); > + > + nbytes = read(fifo_fd, pbuf, pbuf_size); > + if (nbytes < 0) { > + if (errno != EAGAIN) { > + ERROR("Error %d reading FIFO '%s'\n", errno, > + fname); > + } > + nbytes = 0; /* empty fifo */ > + } > + > + /* > + * Ensure FIFO has been drained. > + * > + * TODO: If FIFO has not fully drained, our estimate of > + * unread-bytes is wrong. We could: > + * > + * - have kernel print exact number of unread-bytes > + * in /proc/pid/fdinfo/<fd> > + * > + * - read in contents multiple times and write multiple > + * fifobufs or assemble them into a single, large > + * buffer. > + */ > + ensure_fifo_has_drained(fname, fifo_fd); > + > + /* > + * Save FIFO data to checkpoint file > + */ > + fifofdinfo.fi_fd = fi[i].fdnum; > + fifofdinfo.fi_length = nbytes; > + write_item(fd, "fifofdinfo", &fifofdinfo, sizeof(fifofdinfo)); > + > + if (nbytes) { > + write_item(fd, "fifobufs", pbuf, nbytes); > + > + /* > + * Restore FIFO's contents so checkpointed application > + * won't miss a thing. > + */ > + errno = 0; > + rc = write(fifo_fd, pbuf, nbytes); > + if (rc != nbytes) { > + ERROR("Wrote-back only %d of %d bytes to FIFO, " > + "error %d\n", rc, nbytes, > errno); > + } > + } > + > + close(fifo_fd); > + free(pbuf); > + } > + > + write_item(fd, "END FIFO", NULL, 0); > + > + return 0; > +} > + > static int save_process_data(pid_t pid, int fd, lh_list_t *ptree) > { > char fname[256], exe[256], cwd[256], *argv, *env, *buf; > @@ -587,6 +714,8 @@ static int save_process_data(pid_t pid, int fd, lh_list_t > *ptree) > } > write_item(fd, "END FD", NULL, 0); > > + save_process_fifo_info(pi, fd); > + > /* sockets */ > write_item(fd, "SOCK", NULL, 0); > for (i = 0; i < pi->ns; i++) > @@ -839,6 +968,29 @@ int restore_fd(int fd, pid_t pid) > } > if (pfd != fdinfo->fdnum) t_d(PT_CLOSE(pid, > pfd)); > } > + } else if (S_ISFIFO(fdinfo->mode)) { > + int pipefds[2] = { 0, 0 }; > + > + /* > + * We create the pipe when we see the pipe's read-fd. > + * Just ignore the pipe's write-fd. > + */ > + if (fdinfo->flag == O_WRONLY) > + continue; > + > + DEBUG("Creating pipe for fd %d\n", fdinfo->fdnum); > + > + t_d(PT_PIPE(pid, pipefds)); > + t_d(pipefds[0]); > + t_d(pipefds[1]); > + > + if (pipefds[0] != fdinfo->fdnum) { > + DEBUG("Hmm, new pipe has fds %d, %d " > + "Old pipe had fd %d\n", pipefds[0], > + pipefds[1], fdinfo->fdnum); getchar(); > + exit(1); > + } > + DEBUG("Done creating pipefds[0] %d\n", pipefds[0]); > } > > /* > @@ -847,20 +999,8 @@ int restore_fd(int fd, pid_t pid) > ret = PT_FCNTL(pid, fdinfo->fdnum, F_SETFL, fdinfo->flag); > DEBUG("---- restore_fd() fd %d setfl flag 0x%x, ret %d\n", > fdinfo->fdnum, fdinfo->flag, ret); > - > - > free(fdinfo); > } > - if (1) { > - /* test: force pipe creation */ > - static int first = 1; > - int pipe[2] = { 0, 0 }; > - if (! first) return 0; > - else first = 0; > - t_d(PT_PIPE(pid, pipe)); > - t_d(pipe[0]); > - t_d(pipe[1]); > - } > return 0; > error: > free(fdinfo); > @@ -1231,6 +1371,55 @@ int restore_sig(pid_t pid, struct sigaction *sigact, > sigset_t *sigmask, sigset_t > return 0; > } > > +int restore_fifo(int fd, pid_t pid) > +{ > + char item[64]; > + void *buf = NULL; > + size_t bufsz; > + int ret; > + int fifo_fd; > + char fname[64]; > + int nbytes; > + fifofdinfo_t *fifofdinfo = NULL; > + > + for(;;) { > + ret = read_item(fd, item, sizeof(item), &buf, &bufsz); > + DEBUG("restore_fifo() read item '%.12s'\n", item); > + if ITEM_IS("END FIFO") > + break; > + else ITEM_SET(fifofdinfo, fifofdinfo_t); > + else if ITEM_IS("fifobufs") { > + DEBUG("restore_fifo() bufsz %d, fi_fd %d, length %d\n", > + bufsz, fifofdinfo->fi_fd, > + fifofdinfo->fi_length); > + > + if (!fifofdinfo->fi_length) > + continue; > + > + sprintf(fname, "/proc/%u/fd/%d", pid, > + fifofdinfo->fi_fd); > + > + fifo_fd = open(fname, O_WRONLY|O_NONBLOCK); > + if (fifo_fd < 0) { > + ERROR("Error %d opening FIFO '%s'\n", errno, > + fname); > + } > + > + errno = 0; > + nbytes = write(fifo_fd, buf, bufsz); > + if (nbytes != bufsz) { > + ERROR("Error %d writing to FIFO '%s'\n", > + errno, fname); > + } > + close(fifo_fd); > + } else > + ERROR("Unexpected item, '%s'\n", item); > + } > + DEBUG("restore_fifo() fd %d, len %d, got 'END FIFO'\n", > + fifofdinfo->fi_fd, fifofdinfo->fi_length); > + return 0; > +} > + > static int process_restart(int fd, int mode) > { > char item[64]; > @@ -1314,6 +1503,8 @@ static int process_restart(int fd, int mode) > ptrace_set_thread_area(npid, ldt); > if (cwd) PT_CHDIR(npid, cwd); > restore_fd(fd, npid); > + } else if (ITEM_IS("FIFO")) { > + restore_fifo(fd, npid); > } else if (ITEM_IS("SOCK")) { > restore_sock(fd, npid); > } else if (ITEM_IS("SEMUNDO")) { _______________________________________________ Containers mailing list [EMAIL PROTECTED] https://lists.linux-foundation.org/mailman/listinfo/containers _______________________________________________ Devel mailing list Devel@openvz.org https://openvz.org/mailman/listinfo/devel