Re: [libvirt] [PATCH 1/2] util: Don't fail virGetUserIDByName when user not found
On 12/06/12 10:25, Osier Yang wrote:
On 2012年12月05日 20:03, Christophe Fergeau wrote:
> virGetUserIDByName is documented as returning 1 if the username
> cannot be found. getpwnam_r is documented as returning:
> « 0 or ENOENT or ESRCH or EBADF or EPERM or ... The given name
> or uid was not found. »
> and that:
> « The formulation given above under "RETURN VALUE" is from POSIX.1-2001.
> It does not call "not found" an error, hence does not specify what
> value errno might have in this situation. But that makes it
> impossible to
> recognize errors. One might argue that according to POSIX errno
> should be
> left unchanged if an entry is not found. Experiments on various
> UNIX-like
> systems shows that lots of different values occur in this situation: 0,
> ENOENT, EBADF, ESRCH, EWOULDBLOCK, EPERM and probably others. »
>
> virGetUserIDByName returns an error when the return value of getpwnam_r
> is non-0. However on my RHEL system, getpwnam_r returns ENOENT when the
> requested user cannot be found, which then causes virGetUserID not
> to behave as documented (it returns an error instead of falling back
> to parsing the passed-in value as an uid).
>
> This commit makes virGetUserIDByName ignore the various values listed
> in getpwnam_r manpage and return a 'user not found' result in such
> cases.
> ---
> src/util/util.c | 3 ++-
> 1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/src/util/util.c b/src/util/util.c
> index 2fd0f2c..df1af7e 100644
> --- a/src/util/util.c
> +++ b/src/util/util.c
> @@ -2530,7 +2530,8 @@ virGetUserIDByName(const char *name, uid_t *uid)
> }
> }
>
> - if (rc != 0) {
> + if ((rc != 0)&& (rc != ENOENT)&& (rc != ESRCH)
> +&& (rc != EBADF)&& (rc != EPERM)) {
Correct indention should be:
if ((rc != 0) && (rc != ENOENT) && (rc != ESRCH) &&
(rc != EBADF) && (rc != EPERM))
When I was changing the code the first time, I got rid of this as the
docs for getpwnam_r seemed clear enough to me that this shouldn't be
needed. But I was wrong and I'd rather not reintroduce this ugly and
nondeterministic error checking.
Per the POSIX standard, even these errors are not enough,
should we give up using getpwnam_r/getgrnam_r, and create
helpers using getpwent/getgrent to do the lookup work
ourselves?
Hmm, those look fine to me. I didn't do my research properly when
changing the code the first time.
<...>
The getpwent() function returns a pointer to a passwd structure,
or NULL if there are no more entries or an error occurs. If an
error occurs, errno is set appropriately. If one wants to check
errno after the call, it should be set to zero before the call.
</...>
<...>
ERRORS
EINTR A signal was caught.
EIO I/O error.
EMFILE The maximum number (OPEN_MAX) of files was open already
in the calling process.
ENFILE The maximum number of files was open already in the system.
ENOMEM Insufficient memory to allocate passwd structure.
ERANGE Insufficient buffer space supplied.
</...>
I think it's pretty easy to distiguish NOT FOUND and other error
then.
That's true. I'll look into this and check if it's feasible for us to do
in libvirt.
Regards,
Osier
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