Date: Wed, 4 Oct 2023 11:31:29 -0400 From: Mark Johnston <markj@freebsd.org> To: freebsd-hackers@freebsd.org Cc: rmacklem@freebsd.org Subject: copy_file_range() doesn't update the atime of an empty file Message-ID: <ZR2FUeIhO7DIQIpj@nuc>
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For a while, Jenkins has been complaining that one of the tmpfs tests is failing: https://ci.freebsd.org/job/FreeBSD-main-amd64-test/23814/testReport/junit/sys.fs.tmpfs/times_test/empty/ This has been happening since commit 8113cc827611a88540736c92ced7d3a7020a1723, which converted cat(1) to use copy_file_range(2). The test in question creates an empty file, waits for a second, then cat(1)s it and checks that the file's atime was updated. After the aforementioned commit, the atime is not updated. I believe the essential difference is that a zero-length read(2) results in a call to VOP_READ(), which results in an updated atime even if no bytes were read. For instance, ffs_read() sets IN_ACCESS so long as the routine doesn't return an error. (I'm not sure if the mtime is correspondingly updated upon a zero-length write.) copy_file_range() on the other hand elides calls to VOP_READ/VOP_WRITE when copylen is 0, so the atime doesn't get updated. I wonder if we could at least change it to call VOP_READ in that scenario, as in the untested patch below. Any thoughts? diff --git a/sys/kern/vfs_vnops.c b/sys/kern/vfs_vnops.c index 4e4161ef1a7f..d60608a6d3b9 100644 --- a/sys/kern/vfs_vnops.c +++ b/sys/kern/vfs_vnops.c @@ -3499,7 +3499,7 @@ vn_generic_copy_file_range(struct vnode *invp, off_t *inoffp, xfer -= (*inoffp % blksize); } /* Loop copying the data block. */ - while (copylen > 0 && error == 0 && !eof && interrupted == 0) { + while (error == 0 && !eof && interrupted == 0) { if (copylen < xfer) xfer = copylen; error = vn_lock(invp, LK_SHARED); @@ -3511,7 +3511,7 @@ vn_generic_copy_file_range(struct vnode *invp, off_t *inoffp, curthread); VOP_UNLOCK(invp); lastblock = false; - if (error == 0 && aresid > 0) { + if (error == 0 && (xfer == 0 || aresid > 0)) { /* Stop the copy at EOF on the input file. */ xfer -= aresid; eof = true;
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