iommufd: Add iommufd_ctx_from_fd()

It's common to get a reference to the iommufd context from a given file
descriptor. So adds an API for it. Existing users of this API are compiled
only when IOMMUFD is enabled, so no need to have a stub for the IOMMUFD
disabled case.

Tested-by: Yanting Jiang <yanting.jiang@intel.com>
Reviewed-by: Jason Gunthorpe <jgg@nvidia.com>
Signed-off-by: Yi Liu <yi.l.liu@intel.com>
Link: https://lore.kernel.org/r/20230718135551.6592-21-yi.l.liu@intel.com
Signed-off-by: Alex Williamson <alex.williamson@redhat.com>

diff --git a/drivers/iommu/iommufd/main.c b/drivers/iommu/iommufd/main.c
index 32ce7be..4bbb20d 100644 (file)
--- a/drivers/iommu/iommufd/main.c
+++ b/drivers/iommu/iommufd/main.c
@@ -378,6 +378,30 @@ struct iommufd_ctx *iommufd_ctx_from_file(struct file *file)
 EXPORT_SYMBOL_NS_GPL(iommufd_ctx_from_file, IOMMUFD);
 
 /**
+ * iommufd_ctx_from_fd - Acquires a reference to the iommufd context
+ * @fd: File descriptor to obtain the reference from
+ *
+ * Returns a pointer to the iommufd_ctx, otherwise ERR_PTR. On success
+ * the caller is responsible to call iommufd_ctx_put().
+ */
+struct iommufd_ctx *iommufd_ctx_from_fd(int fd)
+{
+       struct file *file;
+
+       file = fget(fd);
+       if (!file)
+               return ERR_PTR(-EBADF);
+
+       if (file->f_op != &iommufd_fops) {
+               fput(file);
+               return ERR_PTR(-EBADFD);
+       }
+       /* fget is the same as iommufd_ctx_get() */
+       return file->private_data;
+}
+EXPORT_SYMBOL_NS_GPL(iommufd_ctx_from_fd, IOMMUFD);
+
+/**
  * iommufd_ctx_put - Put back a reference
  * @ictx: Context to put back
  */

diff --git a/include/linux/iommufd.h b/include/linux/iommufd.h
index 3a3216c..9657c58 100644 (file)
--- a/include/linux/iommufd.h
+++ b/include/linux/iommufd.h
@@ -54,6 +54,7 @@ void iommufd_ctx_get(struct iommufd_ctx *ictx);
 
 #if IS_ENABLED(CONFIG_IOMMUFD)
 struct iommufd_ctx *iommufd_ctx_from_file(struct file *file);
+struct iommufd_ctx *iommufd_ctx_from_fd(int fd);
 void iommufd_ctx_put(struct iommufd_ctx *ictx);
 bool iommufd_ctx_has_group(struct iommufd_ctx *ictx, struct iommu_group *group);