From 860051f1d1ef7ee995188b852d8da36bce85b1dc Mon Sep 17 00:00:00 2001 From: Rich Ercolani <214141+rincebrain@users.noreply.github.com> Date: Wed, 9 Jun 2021 20:57:57 -0400 Subject: [PATCH] Added error for writing to /dev/ on Linux MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Starting in Linux 5.10, trying to write to /dev/{null,zero} errors out. Prefer to inform people when this happens rather than hoping they guess what's wrong. Reviewed-by: Antonio Russo Reviewed-by: Ahelenia Ziemiańska Reviewed-by: Brian Behlendorf Reviewed-by: John Kennedy Signed-off-by: Rich Ercolani Closes: #11991 --- cmd/zfs/zfs_main.c | 38 ++++++++++++++++++++++++++++++++++-- lib/libzfs/libzfs_sendrecv.c | 1 + 2 files changed, 37 insertions(+), 2 deletions(-) diff --git a/cmd/zfs/zfs_main.c b/cmd/zfs/zfs_main.c index c583053dba..38bfdc91ae 100644 --- a/cmd/zfs/zfs_main.c +++ b/cmd/zfs/zfs_main.c @@ -728,6 +728,32 @@ finish_progress(char *done) pt_header = NULL; } +/* This function checks if the passed fd refers to /dev/null or /dev/zero */ +#ifdef __linux__ +static boolean_t +is_dev_nullzero(int fd) +{ + struct stat st; + fstat(fd, &st); + return (major(st.st_rdev) == 1 && (minor(st.st_rdev) == 3 /* null */ || + minor(st.st_rdev) == 5 /* zero */)); +} +#endif + +static void +note_dev_error(int err, int fd) +{ +#ifdef __linux__ + if (err == EINVAL && is_dev_nullzero(fd)) { + (void) fprintf(stderr, + gettext("Error: Writing directly to /dev/{null,zero} files" + " on certain kernels is not currently implemented.\n" + "(As a workaround, " + "try \"zfs send [...] | cat > /dev/null\")\n")); + } +#endif +} + static int zfs_mount_and_share(libzfs_handle_t *hdl, const char *dataset, zfs_type_t type) { @@ -4572,11 +4598,16 @@ zfs_do_send(int argc, char **argv) err = zfs_send_saved(zhp, &flags, STDOUT_FILENO, resume_token); + if (err != 0) + note_dev_error(errno, STDOUT_FILENO); zfs_close(zhp); return (err != 0); } else if (resume_token != NULL) { - return (zfs_send_resume(g_zfs, &flags, STDOUT_FILENO, - resume_token)); + err = zfs_send_resume(g_zfs, &flags, STDOUT_FILENO, + resume_token); + if (err != 0) + note_dev_error(errno, STDOUT_FILENO); + return (err); } if (flags.skipmissing && !flags.replicate) { @@ -4627,6 +4658,8 @@ zfs_do_send(int argc, char **argv) err = zfs_send_one(zhp, fromname, STDOUT_FILENO, &flags, redactbook); zfs_close(zhp); + if (err != 0) + note_dev_error(errno, STDOUT_FILENO); return (err != 0); } @@ -4703,6 +4736,7 @@ zfs_do_send(int argc, char **argv) nvlist_free(dbgnv); } zfs_close(zhp); + note_dev_error(errno, STDOUT_FILENO); return (err != 0); } diff --git a/lib/libzfs/libzfs_sendrecv.c b/lib/libzfs/libzfs_sendrecv.c index 2ba673fd09..136255786c 100644 --- a/lib/libzfs/libzfs_sendrecv.c +++ b/lib/libzfs/libzfs_sendrecv.c @@ -849,6 +849,7 @@ dump_ioctl(zfs_handle_t *zhp, const char *fromsnap, uint64_t fromsnap_obj, case ERANGE: case EFAULT: case EROFS: + case EINVAL: zfs_error_aux(hdl, "%s", strerror(errno)); return (zfs_error(hdl, EZFS_BADBACKUP, errbuf));