scsi: cxlflash: Transition to application close model

Caching the adapter file descriptor and performing a close on behalf of
an application is a poor design. This is due to the fact that once a
file descriptor in installed, it is free to be altered without the
knowledge of the cxlflash driver. This can lead to inconsistencies
between the application and kernel. Furthermore, the nature of the
former design is more exploitable and thus should be abandoned.

To support applications performing a close on the adapter file that is
associated with a context, a new flag is introduced to the user API to
indicate to applications that they are responsible for the close
following the cleanup (detach) of a context. The documentation is also
updated to reflect this change in behavior.

Inspired-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Matthew R. Ochs <mrochs@linux.vnet.ibm.com>
Acked-by: Manoj N. Kumar <manoj@linux.vnet.ibm.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>

1 files changed, 14 insertions, 5 deletions

diff --git a/include/uapi/scsi/cxlflash_ioctl.h b/include/uapi/scsi/cxlflash_ioctl.h
index 2302f3ce5f86..6bf1f8a022b1 100644
--- a/include/uapi/scsi/cxlflash_ioctl.h
+++ b/include/uapi/scsi/cxlflash_ioctl.h
@@ -39,19 +39,28 @@ struct dk_cxlflash_hdr {
  * at this time, this provides future flexibility.
  */
 #define DK_CXLFLASH_ALL_PORTS_ACTIVE	0x0000000000000001ULL
+#define DK_CXLFLASH_APP_CLOSE_ADAP_FD	0x0000000000000002ULL
 
 /*
- * Notes:
- * -----
+ * General Notes:
+ * -------------
  * The 'context_id' field of all ioctl structures contains the context
  * identifier for a context in the lower 32-bits (upper 32-bits are not
  * to be used when identifying a context to the AFU). That said, the value
  * in its entirety (all 64-bits) is to be treated as an opaque cookie and
  * should be presented as such when issuing ioctls.
+ */
+
+/*
+ * DK_CXLFLASH_ATTACH Notes:
+ * ------------------------
+ * Read/write access permissions are specified via the O_RDONLY, O_WRONLY,
+ * and O_RDWR flags defined in the fcntl.h header file.
  *
- * For DK_CXLFLASH_ATTACH ioctl, user specifies read/write access
- * permissions via the O_RDONLY, O_WRONLY, and O_RDWR flags defined in
- * the fcntl.h header file.
+ * A valid adapter file descriptor (fd >= 0) is only returned on the initial
+ * attach (successful) of a context. When a context is shared(reused), the user
+ * is expected to already 'know' the adapter file descriptor associated with the
+ * context.
  */
 #define DK_CXLFLASH_ATTACH_REUSE_CONTEXT	0x8000000000000000ULL