shaba/ostree
1
0
Fork 0
mirror of https://github.com/ostreedev/ostree.git synced 2025-03-19 22:50:35 +03:00
Code Issues Projects Releases Wiki Activity

deltas: Add a compression size heuristic for endianness detection

Browse Source 
I see when analyzing a delta here that due to byteswapping a negative
compression ratio of 540%, 66%, and 28%.  Let's arbitrarily pick 20%
as a threshold for detecting byetswapping.
This commit is contained in:
Colin Walters 2016-02-25 11:07:30 -05:00
parent 7fdf072710
commit 5345573470
1 changed files with 29 additions and 7 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

36
src/libostree/ostree-repo-static-delta-core.c
View File

@ -705,6 +705,7 @@ _ostree_delta_get_endianness (GVariant *superblock,
{ g_autoptr(GVariant) meta_entries = NULL;
guint n_parts;
guint i;
gboolean is_byteswapped = FALSE;
g_variant_get_child (superblock, 6, "@a" OSTREE_STATIC_DELTA_META_ENTRY_FORMAT, &meta_entries);
n_parts = g_variant_n_children (meta_entries);
@ -721,15 +722,36 @@ _ostree_delta_get_endianness (GVariant *superblock,
total_objects += n_objects;
total_size += size;
total_usize += usize;
if (size > usize)
{
double ratio = ((double)size)/((double)usize);
/* This should really never happen where compressing things makes it more than 50% bigger.
*/
if (ratio > 1.2)
{
is_byteswapped = TRUE;
break;
}
}
}
/* If the average object size is greater than 4GiB, let's assume
* we're dealing with opposite endianness. I'm fairly confident
* no one is going to be shipping peta- or exa- byte size ostree
* deltas, period. Past the gigabyte scale you really want
* bittorrent or something.
*/
if ((total_size / total_objects) > G_MAXUINT32)
if (!is_byteswapped)
{
/* If the average object size is greater than 4GiB, let's assume
* we're dealing with opposite endianness. I'm fairly confident
* no one is going to be shipping peta- or exa- byte size ostree
* deltas, period. Past the gigabyte scale you really want
* bittorrent or something.
*/
if ((total_size / total_objects) > G_MAXUINT32)
{
is_byteswapped = TRUE;
}
}
if (is_byteswapped)
{
switch (G_BYTE_ORDER)
{