Messages in this thread | | | From | "Makhlis, Lev" <> | Subject | RE: [PATCH] [SYSVIPC] Change shm_tot from int to size_t | Date | Fri, 25 Jun 2004 16:56:32 -0500 |
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Andries Brouwer wrote: > On Fri, Jun 25, 2004 at 12:42:26PM -0500, Makhlis, Lev wrote: > > > > Thirdly, shm_tot is transmitted to userspace (via the > SHM_INFO ioctl) > > > as an unsigned long. If it is necessary to make it larger, then we > > > must do something with this ioctl. For example, return -1 there > > > in case the actual value does not fit in an unsigned long. > > > > The SHM_INFO shmctl is actually how I found it in the first place. > > But we have the same situation with many other values. For example, > > shm_ctlmax, shm_ctlall and shm_segsz can all potentially be > 64-bit wide > > in the kernel and are exported into potentially 32-bit > userspace values. > > We don't return -1 for any of those if they don't fit. Is there a > > special reason to do it in this case? > > There is a good reason to do it always. > If one truncates, then the result is always unreliable. > If one replaces a too large value by -1, then any other value > is reliable. >
I've looked around and couldn't find anything that returns -1 as a value (as opposed to returning an error) when the value won't fit in 32 bits. Here's what I've found (assuming a 32-bit app in all cases): * sys_statfs, which fails with EOVERFLOW if any of the values won't fit * sys_sysinfo, which scales the values down up to a PAGE_SIZE factor, and silently truncates them if they are still too large * BLKGETSIZE ioctl, which fails with EFBIG if the kernel itself is 32-bit, but silently truncates if the kernel is 64-bit * BLKGETSIZE64 ioctl, which always silently truncates * HDIO_GETGEO ioctl (.start is ulong), which always silently truncates I'm sure there are some other examples...
What do you think about following the example of sys_statfs in sys_shmctl? - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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