Re: [Xenomai-help] rtdm_mmap_to_user without MMU

[Jan Kiszka <jan.kiszka@domain.hid>]

[-- Attachment #1: Type: text/plain, Size: 2620 bytes --]

Kolja Waschk wrote:
> Hi,
> 
> I finally seem to have a complete solution for my case. It's probably
> still missing one or the other detail, but it starts to work. I only
> added a few lines to ksrc/skins/rtdm/drvlib.c in rtdm_do_mmap:
> 
> 1. Because linux/mm/nommu.c/validate_mmap_request() checks the
> capabilities of the backing dev, and /dev/zero lacks BDI_CAP_MAP_DIRECT
> capability, the /dev/mem has to be used instead of /dev/zero.
> 
>> filp = filp_open("/dev/mem", O_RDWR, 0);
> 
> 2. A get_unmapped_area() f_op has to be provided on nommu systems. It is
> also checked by validate_mmap_request(). I just copy in the pointer from
> old_fops: the /dev/mem f_op->get_unmapped_area simply passes pgoffs.
> 
>> rtdm_mmap_fops.get_unmapped_area = old_fops->get_unmapped_area;
> 
> 3. Since /dev/mem is used, the offset passed to do_mmap() has to
> point to the actual buffer (probably the physical address, for now I
> just used mmap_data->src_vaddr).
> 
>> user_ptr = (void *)do_mmap(filp, (unsigned long)*pptr, len, prot,
>>            MAP_SHARED, mmap_data->src_vaddr);
> 

Nice analysis! I tried to fold your findings into a patch (actually,
they will become two in the end), see below. Please check if it works
for you.

In the meantime I need to verify if switching to /dev/mem comes without
side-effects for CONFIG_MMU. Anyone with a rtdm_mmap/iomap_to_user test
case at hand is welcome to check this, too!

Jan

---------->

diff --git a/ksrc/skins/rtdm/drvlib.c b/ksrc/skins/rtdm/drvlib.c
index 9f1cda8..3f37e75 100644
--- a/ksrc/skins/rtdm/drvlib.c
+++ b/ksrc/skins/rtdm/drvlib.c
@@ -1844,8 +1844,24 @@ static int rtdm_mmap_buffer(struct file *filp, struct vm_area_struct *vma)
 	return ret;
 }
 
+#ifndef CONFIG_MMU
+static unsigned long rtdm_get_unmapped_area(struct file *file,
+					    unsigned long addr,
+					    unsigned long len,
+					    unsigned long pgoff,
+					    unsigned long flags)
+{
+	struct rtdm_mmap_data *mmap_data = filp->private_data;
+
+	return mmap_data->src_vaddr;
+}
+#endif /* !CONFIG_MMU */
+
 static struct file_operations rtdm_mmap_fops = {
 	.mmap = rtdm_mmap_buffer,
+#ifndef CONFIG_MMU
+	.get_unmapped_area = rtdm_get_unmapped_area,
+#endif /* !CONFIG_MMU */
 };
 
 static int rtdm_do_mmap(rtdm_user_info_t *user_info,
@@ -1859,7 +1875,7 @@ static int rtdm_do_mmap(rtdm_user_info_t *user_info,
 
 	XENO_ASSERT(RTDM, xnpod_root_p(), return -EPERM;);
 
-	filp = filp_open("/dev/zero", O_RDWR, 0);
+	filp = filp_open("/dev/mem", O_RDWR, 0);
 	if (IS_ERR(filp))
 		return PTR_ERR(filp);
 


[-- Attachment #2: OpenPGP digital signature --]
[-- Type: application/pgp-signature, Size: 257 bytes --]