Hi,
Thanks for tracking this down. It has been a mystery for a while.
At Sun, 1 Nov 2009 15:02:15 +0100,
Peter Fritzsche wrote:
>
> [1 <text/plain; us-ascii (7bit)>]
> Package: cowbuilder
> Version: 0.57
> Severity: normal
>
> I noticed a quite bad behavior when building multiple packages at the same
> time. The problem seems to be /var/cache/debconf/config.dat. Multiple
> packages
> want to install x11-common which uses these file over debconf. This means
> that
> this file gets locked (i would guess using flock). As this file is a hardlink
> all other files (which are only hardlinks) will be locked too and the install
> fails. This means that the whole build fails due to the usage of cowbuilder.
> This means that cowdancer must also copy files on flock and not only on
> writes.
>
> I think that it has the same problems as fchmod because we are doing it at
> file table level. Maybe a workaround for known debian specific locked files
> can be added before adding cowdancer overrides.
>
> Just added a warning stub.
> [2 flock-warning.patch <text/x-patch; UTF-8 (7bit)>]
> diff --git a/cowdancer.c b/cowdancer.c
> index 3593ced..b79cc8e 100644
> --- a/cowdancer.c
> +++ b/cowdancer.c
> @@ -35,6 +35,7 @@ static int (*origlibc_fchown)(int fd, uid_t, gid_t) = NULL;
> static int (*origlibc_lchown)(const char *, uid_t, gid_t) = NULL;
> static int (*origlibc_chmod)(const char *, mode_t) = NULL;
> static int (*origlibc_fchmod)(int fd, mode_t) = NULL;
> +static int (*origlibc_flock)(int fd, int) = NULL;
>
> static struct ilist_struct* ilist=NULL;
> static long ilist_len=0;
> @@ -200,6 +201,7 @@ static int initialize_functions ()
> origlibc_lchown = dlsym(RTLD_NEXT, "lchown");
> origlibc_chmod = dlsym(RTLD_NEXT, "chmod");
> origlibc_fchmod = dlsym(RTLD_NEXT, "fchmod");
> + origlibc_flock = dlsym(RTLD_NEXT, "flock");
>
> if (getenv("COWDANCER_DEBUG"))
> {
> @@ -606,13 +608,13 @@ int check_fd_inode_and_warn(int fd)
> S_ISREG(buf.st_mode))
> {
> /* Someone opened file read-only, and called
> - fchown/fchmod; I don't really know how to do
> + fchown/fchmod/flock; I don't really know how to do
> salvation in that case, since the original filename is
> probably not available, and file is already open.
>
> If there is any better way, I'd like to know.
> */
> - fprintf(stderr, "W: cowdancer: unsupported operation, read-only open
> and fchown/fchmod: %li:%li\n",
> + fprintf(stderr, "W: cowdancer: unsupported operation, read-only open
> and fchown/fchmod/flock: %li:%li\n",
> (long)buf.st_dev, (long)buf.st_ino);
> /* emit a warning and do not fail,
> if you want to make it fail, add a return 1;
> @@ -708,3 +710,25 @@ int fchmod(int fd, mode_t mode)
> ret = origlibc_fchmod(fd, mode);
> return ret;
> }
> +
> +#undef flock
> +int flock(int fd, int operation)
> +{
> + int ret;
> + if(initialize_functions())
> + {
> + errno=ENOMEM;
> + return -1;
> + }
> + if(!getenv("COWDANCER_IGNORE"))
> + {
> + debug_cowdancer ("flock");
> + if (check_fd_inode_and_warn(fd))
> + {
> + errno=ENOMEM;
> + return -1;
> + }
> + }
> + ret = origlibc_flock(fd, operation);
> + return ret;
> +}
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