qga: Better mapping of SEEK_* in guest-file-seek

Exposing OS-specific SEEK_ constants in our qapi was a mistake
(if the host has SEEK_CUR as 1, but the guest has it as 2, then
the semantics are unclear what should happen); if we had a time
machine, we would instead expose only a symbolic enum.  It's too
late to change the fact that we have an integer in qapi, but we
can at least document what mapping we want to enforce for all
qga clients (and luckily, it happens to be the mapping that both
Linux and Windows use); then fix the code to match that mapping.
It also helps us filter out unsupported SEEK_DATA and SEEK_HOLE.

In the future, we may wish to move our QGA_SEEK_* constants into
qga/qapi-schema.json, along with updating the schema to take an
alternate type (either the integer, or the string value of the
enum name) - but that's too much risk during hard freeze.

Signed-off-by: Eric Blake <eblake@redhat.com>
Signed-off-by: Michael Roth <mdroth@linux.vnet.ibm.com>

1 files changed, 7 insertions, 0 deletions

diff --git a/qga/guest-agent-core.h b/qga/guest-agent-core.h
index e92c6ab..238dc6b 100644
--- a/qga/guest-agent-core.h
+++ b/qga/guest-agent-core.h
@@ -15,6 +15,13 @@
 
 #define QGA_READ_COUNT_DEFAULT 4096
 
+/* Mapping of whence codes used by guest-file-seek. */
+enum {
+    QGA_SEEK_SET = 0,
+    QGA_SEEK_CUR = 1,
+    QGA_SEEK_END = 2,
+};
+
 typedef struct GAState GAState;
 typedef struct GACommandState GACommandState;
 extern GAState *ga_state;