On Wed, Jun 19, 2019 at 12:45:25PM -0400, Jeff Layton wrote: > v2: drop bogus EXPORT_SYMBOL of static function > > The only real difference between this set and the one I sent originally > is the removal of a spurious EXPORT_SYMBOL in the snprintf patch. > > I'm mostly sending this with a wider cc list in an effort to get a > review from the maintainers of the printf code. Basically ceph needs a > snprintf variant that does not NULL terminate in order to handle its > virtual xattrs. > > Joe Perches had expressed some concerns about stack usage in vsnprintf > with this, but I'm not sure I really understand the basis of that > concern. If it is problematic, then I could use suggestions as to how > best to fix that up. It might be problematic, since vsnprintf() can be called recursively. > ----------------------------8<----------------------------- > > kcephfs has several "virtual" xattrs that return strings that are > currently populated using snprintf(), which always NULL terminates the > string. > > This leads to the string being truncated when we use a buffer length > acquired by calling getxattr with a 0 size first. The last character > of the string ends up being clobbered by the termination. So, then don't use snprintf() for this, simple memcpy() designed for that kind of things. > The convention with xattrs is to not store the termination with string > data, given that we have the length. This is how setfattr/getfattr > operate. Fine. > This patch makes ceph's virtual xattrs not include NULL termination > when formatting their values. In order to handle this, a new > snprintf_noterm function is added, and ceph is changed over to use > this to populate the xattr value buffer. In terms of vsnprintf(), and actually compiler point of view, it's not a string anymore, it's a text-based data. Personally, I don't see an advantage of a deep intrusion into vsnprintf(). The wrapper can be made to achieve this w/o touching the generic code. Thus, you can quickly and cleanly fix the issue, while discussing this with wider audience. > Finally, we fix ceph to > return -ERANGE properly when the string didn't fit in the buffer. > > Jeff Layton (3): > lib/vsprintf: add snprintf_noterm > ceph: don't NULL terminate virtual xattr strings > ceph: return -ERANGE if virtual xattr value didn't fit in buffer > > fs/ceph/xattr.c | 49 +++++++------- > include/linux/kernel.h | 2 + > lib/vsprintf.c | 144 ++++++++++++++++++++++++++++------------- > 3 files changed, 129 insertions(+), 66 deletions(-) > > -- > 2.21.0 > -- With Best Regards, Andy Shevchenko
