On Wed, Feb 26, 2020 at 02:39:04PM +0100, Pino Toscano wrote:
select() has a maximum value for the FDs it can monitor, and since the libguestfs library can be used in other applications, this limit may be hit by users in case lots of FDs are opened.
As solution, switch to poll(): it has a slightly better interface to check what changed and for which FD, and it does not have a limit in the value of the FDs monitored.
poll() is supported on the platforms we support, so there is no need to use the gnulib module for it. --- lib/command.c | 54 ++++++++++++++++++++++++++++++++++----------------- 1 file changed, 36 insertions(+), 18 deletions(-)
diff --git a/lib/command.c b/lib/command.c index f2161de9a..13b084934 100644 --- a/lib/command.c +++ b/lib/command.c @@ -89,9 +89,8 @@ #include <signal.h> #include <errno.h> #include <assert.h> -#include <sys/types.h> #include <sys/stat.h> -#include <sys/select.h> +#include <poll.h>
#ifdef HAVE_SYS_TIME_H #include <sys/time.h> @@ -650,37 +649,41 @@ run_child (struct command *cmd) static int loop (struct command *cmd) { - fd_set rset, rset2; - int maxfd = -1, r; + struct pollfd fds[2]; + int r; size_t nr_fds = 0; CLEANUP_FREE char *buf = safe_malloc (cmd->g, BUFSIZ); ssize_t n;
- FD_ZERO (&rset); + memset (&fds, 0, sizeof fds); + + fds[0].fd = cmd->errorfd; + fds[1].fd = cmd->outfd;
if (cmd->errorfd >= 0) { - FD_SET (cmd->errorfd, &rset); - maxfd = MAX (cmd->errorfd, maxfd); + fds[0].events = POLLIN; nr_fds++; }
if (cmd->outfd >= 0) { - FD_SET (cmd->outfd, &rset); - maxfd = MAX (cmd->outfd, maxfd); + fds[1].events = POLLIN; nr_fds++; }
while (nr_fds > 0) { - rset2 = rset; - r = select (maxfd+1, &rset2, NULL, NULL, NULL); + r = poll (fds, 2, -1); if (r == -1) { if (errno == EINTR || errno == EAGAIN) continue; - perrorf (cmd->g, "select"); + perrorf (cmd->g, "poll"); + return -1; + } + if (fds[0].revents & POLLERR || fds[1].revents & POLLERR) { + perrorf (cmd->g, "poll"); return -1; }
- if (cmd->errorfd >= 0 && FD_ISSET (cmd->errorfd, &rset2)) { + if (fds[0].revents & POLLIN) { /* Read output and send it to the log. */ n = read (cmd->errorfd, buf, BUFSIZ); if (n > 0) @@ -689,20 +692,26 @@ loop (struct command *cmd) else if (n == 0) { if (close (cmd->errorfd) == -1) perrorf (cmd->g, "close: errorfd"); - FD_CLR (cmd->errorfd, &rset); + fds[0].fd = -1; cmd->errorfd = -1; nr_fds--; } else if (n == -1) { perrorf (cmd->g, "read: errorfd"); close (cmd->errorfd); - FD_CLR (cmd->errorfd, &rset); + fds[0].fd = -1; cmd->errorfd = -1; nr_fds--; } } + if (fds[0].revents & POLLHUP) { + close (cmd->errorfd); + fds[0].fd = -1; + cmd->errorfd = -1; + nr_fds--; + }
Now fds[0] is -1, and fds[1] is still an open file descriptor. Next time around the loop it will call poll() on 'fds' array which contains this FD == -1. In theory that results in POLLNVAL, but on OS-X at least it causes poll() itself to return an error. I'd initialize 'struct pollfd' inside the loop, such that it only ever contains valid open FDs.
- if (cmd->outfd >= 0 && FD_ISSET (cmd->outfd, &rset2)) { + if (fds[1].revents & POLLIN) { /* Read the output, buffer it up to the end of the line, then * pass it to the callback. */ @@ -716,18 +725,27 @@ loop (struct command *cmd) cmd->outbuf.close_data (cmd); if (close (cmd->outfd) == -1) perrorf (cmd->g, "close: outfd"); - FD_CLR (cmd->outfd, &rset); + fds[1].fd = -1; cmd->outfd = -1; nr_fds--; } else if (n == -1) { perrorf (cmd->g, "read: outfd"); close (cmd->outfd); - FD_CLR (cmd->outfd, &rset); + fds[1].fd = -1; cmd->outfd = -1; nr_fds--; } } + if (fds[1].revents & POLLHUP) { + if (cmd->outbuf.close_data) + cmd->outbuf.close_data (cmd); + if (close (cmd->outfd) == -1) + perrorf (cmd->g, "close: outfd"); + fds[1].fd = -1; + cmd->outfd = -1; + nr_fds--; + } }
return 0; -- 2.24.1
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