On 09/13/19 16:50, Anthony PERARD wrote:
> When doing an action with a path and subpath in the xenstore,
> XenStoreJoin is called to generate "$path/$subpath". But this function
> do an allocation of memory which isn't necessary. Instead we will
> construct the path with WRITE_REQUEST and data used to generate the
> path will be copied directly to the xenstore shared ring.
>
> Also change WRITE_REQUEST.Len type, it only contain sizes and doesn't
> need to be exactly 32bits.
>
> Ref: https://bugzilla.tianocore.org/show_bug.cgi?id=2190
> Signed-off-by: Anthony PERARD <[email protected]>
> ---
> OvmfPkg/XenBusDxe/XenStore.c | 78 +++++++++++++++++++++---------------
> 1 file changed, 46 insertions(+), 32 deletions(-)
>
> diff --git a/OvmfPkg/XenBusDxe/XenStore.c b/OvmfPkg/XenBusDxe/XenStore.c
> index 7b71dc156d..ca7be12d68 100644
> --- a/OvmfPkg/XenBusDxe/XenStore.c
> +++ b/OvmfPkg/XenBusDxe/XenStore.c
> @@ -53,7 +53,7 @@
>
> typedef struct {
> CONST VOID *Data;
> - UINT32 Len;
> + UINTN Len;
> } WRITE_REQUEST;
>
> /* Register callback to watch subtree (node) in the XenStore. */
> @@ -260,6 +260,35 @@ XenStoreFindWatch (
> return NULL;
> }
>
> +/**
> + Fill the first three slots of a WRITE_REQUEST array.
> +
> + When those three slots are concatenated to generate a string, the resulting
> + string will be "$Path\0" or "$Path/$SubPath\0" if SubPath is provided.
> +**/
> +STATIC
> +VOID
> +XenStorePrepareWriteRequest (
> + IN OUT WRITE_REQUEST *WriteRequest,
> + IN CONST CHAR8 *Path,
> + IN CONST CHAR8 *SubPath OPTIONAL
> + )
> +{
> + SetMem(WriteRequest, 3 * sizeof (WRITE_REQUEST), 0);
(1) ZeroMem() is more idiomatic. Also, please insert a space before the
opening paren.
> + WriteRequest[0].Data = Path;
> + WriteRequest[0].Len = AsciiStrSize (Path);
> + if (SubPath != NULL && SubPath[0] != '\0') {
> + //
> + // Remove the \0 from the first part of the request.
> + //
> + WriteRequest[0].Len--;
> + WriteRequest[1].Data = "/";
> + WriteRequest[1].Len = 1;
> + WriteRequest[2].Data = SubPath;
> + WriteRequest[2].Len = AsciiStrSize (SubPath);
> + }
> +}
> +
So this suggests that only the last element in the array should point to
a NUL-terminated string. Strings pointed-to by earlier elements in the
array should not be NUL-terminated. Is that correct?
> //
> // Public Utility Functions
> // API comments for these methods can be found in XenStore.h
> @@ -842,6 +871,7 @@ XenStoreTalkv (
> @param Transaction The transaction to use for this request.
> @param RequestType The type of message to send.
> @param Body The body of the request.
> + @param SubPath If !NULL and not "", "/$SubPath" is append to Body.
> @param LenPtr The returned length of the reply.
> @param Result The returned body of the reply.
>
> @@ -854,16 +884,16 @@ XenStoreSingle (
> IN CONST XENSTORE_TRANSACTION *Transaction,
> IN enum xsd_sockmsg_type RequestType,
> IN CONST CHAR8 *Body,
> + IN CONST CHAR8 *SubPath OPTIONAL,
> OUT UINT32 *LenPtr OPTIONAL,
> OUT VOID **Result OPTIONAL
> )
> {
> - WRITE_REQUEST WriteRequest;
> + WRITE_REQUEST WriteRequest[3];
>
> - WriteRequest.Data = (VOID *) Body;
> - WriteRequest.Len = (UINT32)AsciiStrSize (Body);
> + XenStorePrepareWriteRequest (WriteRequest, Body, SubPath);
>
> - return XenStoreTalkv (Transaction, RequestType, &WriteRequest, 1,
> + return XenStoreTalkv (Transaction, RequestType, WriteRequest, 3,
> LenPtr, Result);
(2) It would be slightly more idiomatic to pass
ARRAY_SIZE (WriteRequest)
in place of the naked 3.
> }
>
> @@ -1113,15 +1143,12 @@ XenStoreListDirectory (
> OUT CONST CHAR8 ***DirectoryListPtr
> )
> {
> - CHAR8 *Path;
> CHAR8 *TempStr;
> UINT32 Len = 0;
> XENSTORE_STATUS Status;
>
> - Path = XenStoreJoin (DirectoryPath, Node);
> - Status = XenStoreSingle (Transaction, XS_DIRECTORY, Path, &Len,
> + Status = XenStoreSingle (Transaction, XS_DIRECTORY, DirectoryPath, Node,
> &Len,
> (VOID **) &TempStr);
> - FreePool (Path);
> if (Status != XENSTORE_STATUS_SUCCESS) {
> return Status;
> }
> @@ -1160,13 +1187,11 @@ XenStoreRead (
> OUT VOID **Result
> )
> {
> - CHAR8 *Path;
> VOID *Value;
> XENSTORE_STATUS Status;
>
> - Path = XenStoreJoin (DirectoryPath, Node);
> - Status = XenStoreSingle (Transaction, XS_READ, Path, LenPtr, &Value);
> - FreePool (Path);
> + Status = XenStoreSingle (Transaction, XS_READ, DirectoryPath, Node,
> + LenPtr, &Value);
(3) Indentation.
> if (Status != XENSTORE_STATUS_SUCCESS) {
> return Status;
> }
> @@ -1183,21 +1208,13 @@ XenStoreWrite (
> IN CONST CHAR8 *Str
> )
> {
> - CHAR8 *Path;
> - WRITE_REQUEST WriteRequest[2];
> - XENSTORE_STATUS Status;
> + WRITE_REQUEST WriteRequest[4];
>
> - Path = XenStoreJoin (DirectoryPath, Node);
> + XenStorePrepareWriteRequest (WriteRequest, DirectoryPath, Node);
> + WriteRequest[3].Data = Str;
> + WriteRequest[3].Len = AsciiStrLen (Str);
Now we have two strings, pointed-to by elements in the array, that are
NUL-terminated: the element at offset 2, and the one at offset 3. Is
that intentional? Is that part of the message framing?
Hmmm... From the original code:
>
> - WriteRequest[0].Data = (VOID *) Path;
> - WriteRequest[0].Len = (UINT32)AsciiStrSize (Path);
> - WriteRequest[1].Data = (VOID *) Str;
> - WriteRequest[1].Len = (UINT32)AsciiStrLen (Str);
That seems to be the case. I guess the first run (offsets 0 through 2)
is parsed until the first NUL is encountered, for "path", then the
second run (3 and onwards) is parsed until the second NUL for "data".
Sounds plausible; OK.
> -
> - Status = XenStoreTalkv (Transaction, XS_WRITE, WriteRequest, 2, NULL,
> NULL);
> - FreePool (Path);
> -
> - return Status;
> + return XenStoreTalkv (Transaction, XS_WRITE, WriteRequest, 4, NULL, NULL);
(4) Please use ARRAY_SIZE(); it's more robust.
> }
>
> XENSTORE_STATUS
> @@ -1207,12 +1224,9 @@ XenStoreRemove (
> IN CONST CHAR8 *Node
> )
> {
> - CHAR8 *Path;
> XENSTORE_STATUS Status;
>
> - Path = XenStoreJoin (DirectoryPath, Node);
> - Status = XenStoreSingle (Transaction, XS_RM, Path, NULL, NULL);
> - FreePool (Path);
> + Status = XenStoreSingle (Transaction, XS_RM, DirectoryPath, Node, NULL,
> NULL);
>
> return Status;
> }
> @@ -1226,7 +1240,7 @@ XenStoreTransactionStart (
> XENSTORE_STATUS Status;
>
> Status = XenStoreSingle (XST_NIL, XS_TRANSACTION_START, "", NULL,
> - (VOID **) &IdStr);
> + NULL, (VOID **) &IdStr);
(5) Indentation.
> if (Status == XENSTORE_STATUS_SUCCESS) {
> Transaction->Id = (UINT32)AsciiStrDecimalToUintn (IdStr);
> FreePool (IdStr);
> @@ -1246,7 +1260,7 @@ XenStoreTransactionEnd (
> AbortStr[0] = Abort ? 'F' : 'T';
> AbortStr[1] = '\0';
>
> - return XenStoreSingle (Transaction, XS_TRANSACTION_END, AbortStr, NULL,
> NULL);
> + return XenStoreSingle (Transaction, XS_TRANSACTION_END, AbortStr, NULL,
> NULL, NULL);
> }
>
> XENSTORE_STATUS
>
With the above addressed:
Reviewed-by: Laszlo Ersek <[email protected]>
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