[PATCH] Use a single mmap interface in libxc

[PATCH] Use a single mmap interface in libxc

[Patrick Colp]

# HG changeset patch
# User Patrick Colp <Patrick.Colp@citrix.com>
# Date 1248081941 -3600
# Node ID 8e1301247d784ffb98b0721d9f6f46daa0640af1
# Parent  91407452cdb62f427c74e227956dc34a107cab46
Use a single mmap interface in libxc.

This patch modifies xc_map_foreign_range and xc_map_foreign_ranges to call
mmap_map_foreign_batch. This eliminates the need for multiple privcmd mmap
ioctls. Now only IOCTL_PRIVCMD_MMAPBATCH is required.

Signed-off-by: Patrick Colp <Patrick.Colp@citrix.com>

diff -r 91407452cdb6 -r 8e1301247d78 tools/libxc/xc_linux.c
--- a/tools/libxc/xc_linux.c	Wed Jul 15 13:15:50 2009 +0100
+++ b/tools/libxc/xc_linux.c	Mon Jul 20 10:25:41 2009 +0100
@@ -92,67 +92,38 @@
                            int size, int prot,
                            unsigned long mfn)
 {
-    privcmd_mmap_t ioctlx;
-    privcmd_mmap_entry_t entry;
-    void *addr;
-    addr = mmap(NULL, size, prot, MAP_SHARED, xc_handle, 0);
-    if ( addr == MAP_FAILED ) {
-        perror("xc_map_foreign_range: mmap failed");
-        return NULL;
-    }
+    xen_pfn_t *arr;
+    int num;
+    int i;
 
-    ioctlx.num=1;
-    ioctlx.dom=dom;
-    ioctlx.entry=&entry;
-    entry.va=(unsigned long) addr;
-    entry.mfn=mfn;
-    entry.npages=(size+PAGE_SIZE-1)>>PAGE_SHIFT;
-    if ( ioctl(xc_handle, IOCTL_PRIVCMD_MMAP, &ioctlx) < 0 )
-    {
-        int saved_errno = errno;
-        perror("xc_map_foreign_range: ioctl failed");
-        (void)munmap(addr, size);
-        errno = saved_errno;
-        return NULL;
-    }
-    return addr;
+    num = (size + PAGE_SIZE - 1) >> PAGE_SHIFT;
+    arr = calloc(num, sizeof(xen_pfn_t));
+
+    for ( i = 0; i < num; i++ )
+        arr[i] = mfn + i;
+
+    return xc_map_foreign_batch(xc_handle, dom, prot, arr, num);
 }
 
 void *xc_map_foreign_ranges(int xc_handle, uint32_t dom,
                             size_t size, int prot, size_t chunksize,
                             privcmd_mmap_entry_t entries[], int nentries)
 {
-    privcmd_mmap_t ioctlx;
-    int i, rc;
-    void *addr;
+    xen_pfn_t *arr;
+    int num_per_entry;
+    int num;
+    int i;
+    int j;
 
-    addr = mmap(NULL, size, prot, MAP_SHARED, xc_handle, 0);
-    if ( addr == MAP_FAILED )
-        goto mmap_failed;
+    num_per_entry = chunksize >> PAGE_SHIFT;
+    num = num_per_entry * nentries;
+    arr = calloc(num, sizeof(xen_pfn_t));
 
     for ( i = 0; i < nentries; i++ )
-    {
-        entries[i].va = (unsigned long)addr + (i * chunksize);
-        entries[i].npages = chunksize >> PAGE_SHIFT;
-    }
+        for ( j = 0; j < num_per_entry; j++ )
+            arr[i * num_per_entry + j] = entries[i].mfn + j;
 
-    ioctlx.num   = nentries;
-    ioctlx.dom   = dom;
-    ioctlx.entry = entries;
-
-    rc = ioctl(xc_handle, IOCTL_PRIVCMD_MMAP, &ioctlx);
-    if ( rc )
-        goto ioctl_failed;
-
-    return addr;
-
-ioctl_failed:
-    rc = munmap(addr, size);
-    if ( rc == -1 )
-        ERROR("%s: error in error path\n", __FUNCTION__);
-
-mmap_failed:
-    return NULL;
+    return xc_map_foreign_batch(xc_handle, dom, prot, arr, num);
 }
 
 static int do_privcmd(int xc_handle, unsigned int cmd, unsigned long data)

Re: [PATCH] Use a single mmap interface in libxc

[Keir Fraser]

On 20/07/2009 10:27, "Patrick Colp" <Patrick.Colp@citrix.com> wrote:

> # HG changeset patch
> # User Patrick Colp <Patrick.Colp@citrix.com>
> # Date 1248081941 -3600
> # Node ID 8e1301247d784ffb98b0721d9f6f46daa0640af1
> # Parent  91407452cdb62f427c74e227956dc34a107cab46
> Use a single mmap interface in libxc.
> 
> This patch modifies xc_map_foreign_range and xc_map_foreign_ranges to call
> mmap_map_foreign_batch. This eliminates the need for multiple privcmd mmap
> ioctls. Now only IOCTL_PRIVCMD_MMAPBATCH is required.

Some explanation of why this is a useful improvement would be nice.

 -- Keir

Re: [PATCH] Use a single mmap interface in libxc

[Patrick Colp]

The idea is that the privcmd interface can also only have one mmap function 
instead of two (something to be done to privcmd in pvops). This simplifies 
things and removes unnecessary redundant code. While map_batch might not be the 
ideal interface, I think it's a step in the right direction, anyway.

Also, for the project I'm working on, I need to intercept mmap calls. This 
required me to have to put similar code in two places and, as it turned out, 
modifying the mmap_foreign_range functions was going to be difficult. mmap_batch 
can do everything required for map_foreign_range (and more), so it seemed like 
the thing to do was to use that for everything so there was just the one call 
into privcmd (and just one spot to edit code).


Patrick


Keir Fraser wrote:
> On 20/07/2009 10:27, "Patrick Colp" <Patrick.Colp@citrix.com> wrote:
> 
>> # HG changeset patch
>> # User Patrick Colp <Patrick.Colp@citrix.com>
>> # Date 1248081941 -3600
>> # Node ID 8e1301247d784ffb98b0721d9f6f46daa0640af1
>> # Parent  91407452cdb62f427c74e227956dc34a107cab46
>> Use a single mmap interface in libxc.
>>
>> This patch modifies xc_map_foreign_range and xc_map_foreign_ranges to call
>> mmap_map_foreign_batch. This eliminates the need for multiple privcmd mmap
>> ioctls. Now only IOCTL_PRIVCMD_MMAPBATCH is required.
> 
> Some explanation of why this is a useful improvement would be nice.
> 
>  -- Keir
> 
>