selftests/memfd/fuse_test.c

1 // SPDX-License-Identifier: GPL-2.0
3  * memfd GUP test-case
5  * fuse_mnt.c program to provide a fake direct-IO FUSE mount-point for us. This
6  * file-system delays _all_ reads by 1s and forces direct-IO. This means, any
7  * read() on files in that file-system will pin the receive-buffer pages for at
10  * We use this trick to race ADD_SEALS against a write on a memfd object. The
12  * the read() syscall with our memory-mapped memfd object as receive buffer to
34 #include <sys/wait.h>
97 		printf("ADD_SEALS(%d, %llu -> %llu) failed: %m\n",  in mfd_assert_add_seals()
116 		printf("ADD_SEALS(%d, %llu -> %llu) didn't fail as expected with EBUSY: %m\n",  in mfd_busy_add_seals()
160 static int global_mfd = -1;
170 	 * SEAL_WRITE. This _must_ fail as the parent thread has a read() into  in sealing_thread_fn()
172 	 * We then wait one more second and try sealing again. This time it  in sealing_thread_fn()
176 	/* wait 200ms for FUSE-request to be active */  in sealing_thread_fn()
184 	 * implement page-replacements or other fancy ways to avoid racing  in sealing_thread_fn()
190 		/* wait 1s more so the FUSE-request is done */  in sealing_thread_fn()
237 		printf("error: please pass path to file in fuse_mnt mount-point\n");  in main()
268 	/* create new memfd-object */  in main()
273 	/* mmap memfd-object for writing */  in main()
276 	/* pass mfd+mapping to a separate sealing-thread which tries to seal  in main()
282 	/* Use read() on the FUSE file to read into our memory-mapped memfd  in main()
284 	 * memfd-object.  in main()
285 	 * If @fd is on the memfd-fake-FUSE-FS, the read() is delayed by 1s.  in main()
286 	 * This guarantees that the receive-buffer is pinned for 1s until the  in main()
289 	r = read(fd, p, mfd_def_size);  in main()
291 		printf("read() failed: %m\n");  in main()
294 		printf("unexpected EOF on read()\n");  in main()
300 	/* Wait for sealing-thread to finish and verify that it  in main()
305 	/* *IF* the memfd-object was sealed at the time our read() returned,  in main()
306 	 * then the kernel did a page-replacement or canceled the read() (or  in main()
309 	 * In case the memfd-object was *not* sealed, the read() was successfull  in main()
312 	 * in this test-cases, we have explicit 200ms delays which should be  in main()
313 	 * enough to avoid any in-flight writes. */  in main()
317 		printf("memfd sealed during read() but data not discarded\n");  in main()
320 		printf("memfd sealed after read() but data discarded\n");  in main()