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Delete lock file if contained pid is stale #9

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Delete lock file if contained pid is stale #9

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0aa6458
serial: atomically create lock files
a3f May 4, 2019
05c9da8
serial: create lock files in HDB UUCP format
a3f May 4, 2019
91a6aec
serial: delete stale lock files
a3f May 4, 2019
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62 changes: 43 additions & 19 deletions serial.c
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Original file line number Diff line number Diff line change
Expand Up @@ -22,6 +22,7 @@

#include <limits.h>
#include <sys/ioctl.h>
#include <errno.h>
#include <arpa/telnet.h>

#include "microcom.h"
Expand Down Expand Up @@ -177,29 +178,52 @@ struct ios_ops * serial_init(char *device)
exit(1);
}

fd = open(lockfile, O_RDONLY);
if (fd >= 0 && !opt_force) {
close(fd);
main_usage(3, "lockfile for port exists", device);
}
relock:
fd = open(lockfile, O_RDWR | O_CREAT | O_EXCL, 0444);
if (fd < 0) {
if (errno == EEXIST) {
char pidbuf[12];
ssize_t nbytes = 0;
if (opt_force) {
printf("lockfile for port exists, ignoring\n");
serial_unlock();
goto relock;
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@ukleinek ukleinek Aug 25, 2019

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if serial_unlock() fails to delete the lockfile, this is an endless loop.

}

fd = open(lockfile, O_RDONLY);
if (fd < 0)
main_usage(3, "lockfile for port can't be opened", device);

do {
ret = read(fd, &pidbuf[nbytes], sizeof(pidbuf) - nbytes - 1);
nbytes += ret;
} while (ret > 0 && nbytes < sizeof (pidbuf) - 1);
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@ukleinek ukleinek Aug 25, 2019

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Would it make sense here to do some additional checks on the format? E.g. check you read the file completely? If the lockfile happens to be created by an older microcom with pid 33333333 you check for pid 3333 instead. (I think, didn't test.)


if (ret >= 0) {
pidbuf[nbytes] = '\0';
ret = sscanf(pidbuf, "%10ld\n", &pid);

if (ret == 1 && kill(pid, 0) < 0 && errno == ESRCH) {
printf("lockfile contains stale pid, ignoring\n");
serial_unlock();
goto relock;
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@ukleinek ukleinek Aug 25, 2019

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same issue as with the first patch in this series (i.e. endless loop if serial_unlock fails to remove lockfile)

}
}

main_usage(3, "lockfile for port exists", device);
}

if (opt_force) {
printf("cannot create lockfile. ignoring\n");
lockfile = NULL;
goto force;
}

if (fd >= 0 && opt_force) {
close(fd);
printf("lockfile for port exists, ignoring\n");
serial_unlock();
main_usage(3, "cannot create lockfile", device);
}

fd = open(lockfile, O_RDWR | O_CREAT, 0444);
if (fd < 0 && opt_force) {
printf("cannot create lockfile. ignoring\n");
lockfile = NULL;
goto force;
}
if (fd < 0)
main_usage(3, "cannot create lockfile", device);
/* Kermit wants binary pid */
pid = getpid();
write(fd, &pid, sizeof(long));
dprintf(fd, "%10ld\n", (long)pid);
close(fd);
force:
/* open the device */
Expand Down