[PATCH v15 20/26] iommufd: Add iommufd_ctx_from_fd()

[Yi Liu <yi.l.liu@xxxxxxxxx>]

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.

Signed-off-by: Yi Liu <yi.l.liu@xxxxxxxxx>
---
 drivers/iommu/iommufd/main.c | 24 ++++++++++++++++++++++++
 include/linux/iommufd.h      |  1 +
 2 files changed, 25 insertions(+)

diff --git a/drivers/iommu/iommufd/main.c b/drivers/iommu/iommufd/main.c
index 32ce7befc8dd..4bbb20dff430 100644
--- a/drivers/iommu/iommufd/main.c
+++ b/drivers/iommu/iommufd/main.c
@@ -377,6 +377,30 @@ 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 3a3216cb9482..9657c58813dc 100644
--- 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);
 
-- 
2.34.1