From be3245e22d227ad68ab97785d506561374daa028 Mon Sep 17 00:00:00 2001 From: Quentin Monnet Date: Tue, 18 Dec 2018 10:13:18 +0000 Subject: [PATCH] tools: bpftool: attempt to mount tracefs if required for tracelog cmd As a follow-up to commit 30da46b5dc3a ("tools: bpftool: add a command to dump the trace pipe"), attempt to mount the tracefs virtual file system if it is not detected on the system before trying to dump content of the tracing pipe on an invocation of "bpftool prog tracelog". Usually, tracefs in automatically mounted by debugfs when the user tries to access it (e.g. "ls /sys/kernel/debug/tracing" mounts the tracefs). So if we failed to find it, it is probably that debugfs is not here either. Therefore, we just attempt a single mount, at a location that does not involve debugfs: /sys/kernel/tracing. Suggested-by: Daniel Borkmann Signed-off-by: Quentin Monnet Reviewed-by: Jakub Kicinski Signed-off-by: Daniel Borkmann --- tools/bpf/bpftool/common.c | 25 ++++++++++++++++++++----- tools/bpf/bpftool/main.h | 2 ++ tools/bpf/bpftool/tracelog.c | 20 +++++++++++++------- 3 files changed, 35 insertions(+), 12 deletions(-) diff --git a/tools/bpf/bpftool/common.c b/tools/bpf/bpftool/common.c index 24582e8..1bad660 100644 --- a/tools/bpf/bpftool/common.c +++ b/tools/bpf/bpftool/common.c @@ -76,7 +76,8 @@ void set_max_rlimit(void) setrlimit(RLIMIT_MEMLOCK, &rinf); } -static int mnt_bpffs(const char *target, char *buff, size_t bufflen) +static int +mnt_fs(const char *target, const char *type, char *buff, size_t bufflen) { bool bind_done = false; @@ -98,15 +99,29 @@ static int mnt_bpffs(const char *target, char *buff, size_t bufflen) bind_done = true; } - if (mount("bpf", target, "bpf", 0, "mode=0700")) { - snprintf(buff, bufflen, "mount -t bpf bpf %s failed: %s", - target, strerror(errno)); + if (mount(type, target, type, 0, "mode=0700")) { + snprintf(buff, bufflen, "mount -t %s %s %s failed: %s", + type, type, target, strerror(errno)); return -1; } return 0; } +int mount_tracefs(const char *target) +{ + char err_str[ERR_MAX_LEN]; + int err; + + err = mnt_fs(target, "tracefs", err_str, ERR_MAX_LEN); + if (err) { + err_str[ERR_MAX_LEN - 1] = '\0'; + p_err("can't mount tracefs: %s", err_str); + } + + return err; +} + int open_obj_pinned(char *path, bool quiet) { int fd; @@ -162,7 +177,7 @@ int mount_bpffs_for_pin(const char *name) /* nothing to do if already mounted */ goto out_free; - err = mnt_bpffs(dir, err_str, ERR_MAX_LEN); + err = mnt_fs(dir, "bpf", err_str, ERR_MAX_LEN); if (err) { err_str[ERR_MAX_LEN - 1] = '\0'; p_err("can't mount BPF file system to pin the object (%s): %s", diff --git a/tools/bpf/bpftool/main.h b/tools/bpf/bpftool/main.h index 9487345..9e4499c 100644 --- a/tools/bpf/bpftool/main.h +++ b/tools/bpf/bpftool/main.h @@ -98,6 +98,8 @@ void usage(void) __noreturn; void set_max_rlimit(void); +int mount_tracefs(const char *target); + struct pinned_obj_table { DECLARE_HASHTABLE(table, 16); }; diff --git a/tools/bpf/bpftool/tracelog.c b/tools/bpf/bpftool/tracelog.c index 1fa8e51..2dc36df 100644 --- a/tools/bpf/bpftool/tracelog.c +++ b/tools/bpf/bpftool/tracelog.c @@ -54,7 +54,7 @@ find_tracefs_mnt_single(unsigned long magic, char *mnt, const char *mntpt) return true; } -static bool find_tracefs_pipe(char *mnt) +static bool get_tracefs_pipe(char *mnt) { static const char * const known_mnts[] = { "/sys/kernel/debug/tracing", @@ -88,7 +88,17 @@ static bool find_tracefs_pipe(char *mnt) fclose(fp); /* The string from fscanf() might be truncated, check mnt is valid */ - if (!found || validate_tracefs_mnt(mnt, TRACEFS_MAGIC)) + if (found && validate_tracefs_mnt(mnt, TRACEFS_MAGIC)) + goto exit_found; + + p_info("could not find tracefs, attempting to mount it now"); + /* Most of the time, tracefs is automatically mounted by debugfs at + * /sys/kernel/debug/tracing when we try to access it. If we could not + * find it, it is likely that debugfs is not mounted. Let's give one + * attempt at mounting just tracefs at /sys/kernel/tracing. + */ + strcpy(mnt, known_mnts[1]); + if (mount_tracefs(mnt)) return false; exit_found: @@ -115,17 +125,13 @@ int do_tracelog(int argc, char **argv) .sa_handler = exit_tracelog }; char trace_pipe[PATH_MAX]; - bool found_trace_pipe; size_t buff_len = 0; if (json_output) jsonw_start_array(json_wtr); - found_trace_pipe = find_tracefs_pipe(trace_pipe); - if (!found_trace_pipe) { - p_err("could not find trace pipe, tracefs not mounted?"); + if (!get_tracefs_pipe(trace_pipe)) return -1; - } trace_pipe_fd = fopen(trace_pipe, "r"); if (!trace_pipe_fd) { -- 2.7.4