githubmirror/nvme-cli

src/dashboard.c
954 строки25 KB
Daniel Wagner
nvme: move source code to src folder
07 авг 2026, 17:49
07 авг 2026, 17:4908f3fa8
// SPDX-License-Identifier: GPL-2.0-or-later
/*
 * dashboard.c : Generic implementation for live dashboard.
 *
 * Copyright (c) 2026 Nilay Shroff, IBM
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public License
 * as published by the Free Software Foundation; either version 2
 * of the License, or (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 */

#include <stdio.h>
#include <signal.h>
#include <sys/select.h>
#include <sys/ioctl.h>
#include <termios.h>
#include <unistd.h>
#include <string.h>
#include <errno.h>
#include <stdbool.h>
#include <time.h>
#include <stdlib.h>
#include <fcntl.h>
#include <linux/netlink.h>
#include <sys/socket.h>
#include <asm/types.h>

#include "sig-util.h"
#include "common.h"
#include "nvme-print.h"
#include "dashboard.h"

#define NSEC_PER_SEC	1000000000L

struct win_frame {
	/* num of data rows which could fit in visible frame */
	int data_rows;

	/* Header start offset in window frame (always 0) */
	int header_start_off;

	/* data start offset in window frame */
	int data_start_off;

	/* footer start offset in window frame */
	int footer_start_off;

	/* Total num of rows in window frame */
	int rows;
};

struct data_store {
	/* mem-stream backing the buffer */
	FILE *stream;

	/* data buffer which is dynamically allocated by mem-stream  */
	char *buf;
	/* buffer length */
	size_t len;

	/* per-row offsets into the data buffer */
	size_t *row_off;

	/* header, data, footer, and total rows */
	int header_rows;
	int data_rows;
	int footer_rows;
	int num_rows;

	/*
	 * Index of the first data row to display. It can be adjusted
	 * if user navigates/scrolls the screen using arrow keys.
	 * Range: [0 - data_rows).
	 */
	int data_start_idx;

	/* highlighted rows (reverse-video) */
	int rev_header_row;
	int rev_data_row;
	int rev_footer_row;
};

struct dashboard_ctx {
	struct data_store ds;	/* data store */
	struct win_frame frame;	/* window frame */
	int interval;		/* nvme top refresh interval in seconds */
	struct timespec rem_interval;	/* remaining refresh interval */
	int uevent_fd;		/* kernel uevent fd */
	int term_fd;		/* controlling terminal fd */
	sigset_t orig_set;	/* original signal mask of the calling thread */
	struct termios orig_ts;	/* original termio settings of the controlling terminal */
};

/*
 * The following comments describes how this generic dashboard implementation
 * renders data using a fixed-size window frame backed by a potentially larger
 * data store buffer. It clarifies offsets, row calculations, and scrolling
 * behavior:
 *
 * Window Frame Layout (struct win_frame):
 * ======================================
 *    _ _ _ _ _ _ _ _ _ _ _ _ _ _ header_start_off
 *  /            _ _ _ _ _ _ _ _  data_start_off
 * |           /             _ _  footer_start_off
 * |          |            /
 * |          |            |
 * v_ _ _ _ _ v _ _ _ _ _ _v_ _ _ _ _ _
 * |          |            |           |
 * |  header  |    data    |   footer  |
 * |_ _ _ _ _ |_ _ _ _ _ _ |_ _ _ _ _ _|
 * |<-------->|<---------->|<---------->
 *                  ^     ^
 *                  |     |
 *                  |     \_ _ last_data_row
 *                  \_ _ data_rows
 *
 * - The window frame represents the visible terminal screen area. It is
 *   logically divided into three contiguous regions/sections:
 *   header, data and footer.
 * - The window frame size is limited by the terminal dimensions.
 * - Header and footer sizes are fixed per dashboard layout.
 * - The data area (includes area remaining after we account for space needed
 *   for header and footer from the terminal screen area) expands or shrinks
 *   based on available screen space.
 *
 * Data Store Buffer Layout (struct data_store):
 * =============================================
 *    _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _  header_start_off
 *  /            _ _ _ _ _ _ _ _ _ _ _ data_start_off
 * |           /                    _ _footer_start_off
 * |          |                   /
 * |          |                  |
 * v_ _ _ _ _ v_ _ _ _ _ _ _ _ _ v_ _ _ _ _ _
 * |          |                  |           |
 * |  header  |       data       |   footer  |
 * |_ _ _ _ _ |_ _ _ _ _ _ _ _ _ |_ _ _ _ _ _|
 * |<-------->|<---------------->|<--------->|
 * |    ^     ^          ^             ^     |
 * |    |     |          |             |     |
 * |    | data_start_idx |             \_ _ _|_footer_rows
 * |    |                \_ _ _data_rows     |
 * |    \_ _ _header_rows                    |
 * |                                         |
 * |<----------------num_rows -------------->|
 *
 *
 * - The data store buffer holds the complete dashboard content generated at
 *   each refresh interval. Its size may exceed the window frame, enabling
 *   scrolling.
 * - Represents the full logical dashboard content.
 * - Used as the authoritative source for rendering.
 * - Scrolling adjusts which portion of the data area is mapped into the
 *   window frame.
 *
 * Relationship Between window frame and data store:
 * =================================================
 *  - The data store is transposed onto the window frame at render time.
 *
 *  a) Fixed relationship:
 *     - Header always starts at offset 0.
 *       In window frame, frame->header_start_off = 0
 *       In data store, header_start_off = 0
 *
 *     - Header height is constant.
 *       In window frame, frame->data_start_off = ds->header_rows
 *       In data store, data_start_off = ds->header_rows + ds->data_start_idx
 *
 *  b) Footer placement:
 *     - In the data store,
 *       footer_start_off = ds->header_rows + ds->data_rows
 *
 *     - In the window frame,
 *       frame->footer_start_off = frame->data_start_off + frame->data_rows
 *
 *     These two offsets (footer_start_off in data store and frame->footer_
 *     start_off) may differ if the frame cannot display all data rows.
 *
 *  c) Scrolling Semantics:
 *     - Scrolling affects only ds->data_start_idx.
 *     - Header and footer remain pinned and are never scrolled.
 *     - The frame’s data area acts as a viewport into the data store’s data
 *       region.
 *     - The ds->data_start_idx is adjusted based on the terminal scrolling.
 *       For the first time when dashboard is displayed typically the value of
 *       ds->data_start_idx is zero, but then if user scrolls the window then
 *       ds->data_start_idx would be updated. The ds->data_start_idx should be
 *       never set to less than zero and it should never execeed the num of data
 *       rows available in the data staore buffer.
 *
 *  d) Last visible data row in window frame:
 *
 *     If in case window frame data area size is greater than the data store
 *     data area then we would left with some empty space/rows in data area of
 *     window frame. So we then clear the empty space beofre start drawing the
 *     footer.
 *
 *     last_data_row = ds->header_rows + frame->data_rows
 *     If last_data_row > ds->data_rows,
 *     - The remaining frame rows are cleared.
 *     - Footer is drawn immediately after the cleared region.
 *
 * Reverse-Video Highlighting:
 * ===========================
 *  The following fields indicate rows that should be rendered using reverse
 *  video:
 *  - rev_header_row
 *  - rev_data_row
 *  - rev_footer_row
 *  These are relative to their respective sections and allow focused
 *  highlighting.
 */

static void tty_reset(int fd, struct termios *ts)
{
	if (tcsetattr(fd, TCSANOW, ts) < 0)
		nvme_show_perror("reset terminal attributes");
}

static int tty_set_raw(int fd, struct termios *ots)
{
	struct termios ts;

	if (tcgetattr(fd, &ts) < 0) {
		nvme_show_perror("get terminal attributes");
		return -1;
	}

	*ots = ts;

	ts.c_lflag &= ~(ICANON | ECHO);
	ts.c_cc[VMIN] = 1;
	ts.c_cc[VTIME] = 0;

	if (tcsetattr(fd, TCSAFLUSH, &ts) < 0) {
		nvme_show_perror("set terminal attributes");
		return -1;
	}

	return 0;
}

int dashboard_get_interval(struct dashboard_ctx *db_ctx)
{
	return db_ctx->interval;
}

int dashboard_get_header_rows(struct dashboard_ctx *db_ctx)
{
	return db_ctx->ds.header_rows;
}

void dashboard_set_header_rows(struct dashboard_ctx *db_ctx, int rows)
{
	db_ctx->ds.header_rows = rows;
}

int dashboard_get_footer_rows(struct dashboard_ctx *db_ctx)
{
	return db_ctx->ds.footer_rows;
}

void dashboard_set_footer_rows(struct dashboard_ctx *db_ctx, int rows)
{
	db_ctx->ds.footer_rows = rows;
}

int dashboard_get_data_rows(struct dashboard_ctx *db_ctx)
{
	return db_ctx->ds.data_rows;
}

int dashboard_get_data_start(struct dashboard_ctx *db_ctx)
{
	return db_ctx->ds.data_start_idx;
}

int dashboard_set_data_start(struct dashboard_ctx *db_ctx, int off)
{
	if (off >= db_ctx->ds.data_rows)
		return -EINVAL;

	db_ctx->ds.data_start_idx = off;

	return 0;
}

int dashboard_get_frame_data_rows(struct dashboard_ctx *db_ctx)
{
	return db_ctx->frame.data_rows;
}

void dashboard_set_data_row_reverse(struct dashboard_ctx *db_ctx, int row)
{
	db_ctx->ds.rev_data_row = row;
}

void dashboard_reset_data_row_reverse(struct dashboard_ctx *db_ctx)
{
	db_ctx->ds.rev_data_row = -1;
}

void dashboard_set_header_row_reverse(struct dashboard_ctx *db_ctx, int row)
{
	db_ctx->ds.rev_header_row = row;
}

void dashboard_reset_header_row_reverse(struct dashboard_ctx *db_ctx)
{
	db_ctx->ds.rev_header_row = -1;
}

void dashboard_set_footer_row_reverse(struct dashboard_ctx *db_ctx, int row)
{
	db_ctx->ds.rev_footer_row = row;
}

void dashboard_reset_footer_row_reverse(struct dashboard_ctx *db_ctx)
{
	db_ctx->ds.rev_footer_row = -1;
}

static void calc_rem_time(struct dashboard_ctx *db_ctx, struct timespec *start)
{
	struct timespec now;
	__u64 interval_ns, rem_interval_ns, elapsed_ns;
	__u64 start_time_ns, cur_time_ns;

	clock_gettime(CLOCK_MONOTONIC, &now);
	cur_time_ns = (__u64)now.tv_sec * NSEC_PER_SEC + now.tv_nsec;
	start_time_ns = (__u64)start->tv_sec * NSEC_PER_SEC + start->tv_nsec;
	if (cur_time_ns < start_time_ns)
		goto zero;

	interval_ns = (__u64)db_ctx->interval * NSEC_PER_SEC;
	elapsed_ns = cur_time_ns - start_time_ns;
	if (elapsed_ns >= interval_ns)
		goto zero;

	rem_interval_ns = interval_ns - elapsed_ns;

	db_ctx->rem_interval.tv_sec = rem_interval_ns / NSEC_PER_SEC;
	db_ctx->rem_interval.tv_nsec = rem_interval_ns % NSEC_PER_SEC;

	return;
zero:
	db_ctx->rem_interval.tv_sec = 0;
	db_ctx->rem_interval.tv_nsec = 0;
}

static int wait_for_event(struct dashboard_ctx *db_ctx,
		unsigned char *c, bool esc_seq)
{
	fd_set set;
	struct timespec ts, t0;
	int ret, interval_sec, interval_nsec;
	int term_fd = db_ctx->term_fd;
	int uevent_fd = db_ctx->uevent_fd;
	int max_fd = (term_fd > uevent_fd) ? term_fd : uevent_fd;

	/* For escape sequence read, we wait for up to 1 ms. */
	if (esc_seq) {
		interval_sec = 0;
		interval_nsec = 1000000;
	} else {
		/*
		 * If previous pselect() woke up prematurely (might be due to
		 * due to a key pressed other than allowed-key or non-nvme
		 * uevent) then sleep for the remaining interval.
		 */
		if (db_ctx->rem_interval.tv_sec
		    || db_ctx->rem_interval.tv_nsec) {
			interval_sec = db_ctx->rem_interval.tv_sec;
			interval_nsec = db_ctx->rem_interval.tv_nsec;
		} else {
			interval_sec = db_ctx->interval;
			interval_nsec = 0;
		}
	}

	/*
	 * While parsing an escape sequence, only wait for the remaining escape
	 * bytes and thus exclude montioring kobject uevent and sigwinch.
	 * Deferring uevents and SIGWINCH avoids treating non-key events as
	 * escape-sequence bytes.
	 */
	while (1) {
		FD_ZERO(&set);
		FD_SET(term_fd, &set);
		if (!esc_seq)
			FD_SET(uevent_fd, &set);
again:
		ts.tv_sec = interval_sec;
		ts.tv_nsec = interval_nsec;

		/*
		 * Store the time when we start pselect; we may use it later to
		 * compute the remaining time to sleep in case pselect breaks
		 * out prematurely (maybe due to interrupted syscall or due to
		 * any user input).
		 */
		clock_gettime(CLOCK_MONOTONIC, &t0);

		ret = pselect(max_fd + 1, &set, NULL, NULL, &ts,
				esc_seq ? NULL : &db_ctx->orig_set);
		if (ret < 0) {
			if (errno == EINTR) {
				/* Interrupted, signal is received ? */
				if (shr_sigint_received)
					return EVENT_TYPE_KEY_QUIT;

				if (shr_sigwinch_received) {
					struct winsize ws;

					if (ioctl(db_ctx->term_fd, TIOCGWINSZ,
							&ws) < 0)
						return -1;

					db_ctx->frame.rows = ws.ws_row;
					shr_sigwinch_received = false;

					/*
					 * Returning 0 would force screen redraw
					 * based on the updated window size.
					 */
					return EVENT_TYPE_SIGWINCH;
				}

				/* compute remaining time */
				calc_rem_time(db_ctx, &t0);
				interval_sec = db_ctx->rem_interval.tv_sec;
				interval_nsec = db_ctx->rem_interval.tv_nsec;

				goto again;
			}

			nvme_show_perror("pselect");
			return EVENT_TYPE_ERROR;
		}

		if (ret == 0) {/* timed out waiting */
			db_ctx->rem_interval.tv_sec = 0;
			db_ctx->rem_interval.tv_nsec = 0;
			return EVENT_TYPE_TIMEOUT;
		}

		if (!esc_seq) {
			calc_rem_time(db_ctx, &t0);
			interval_sec = db_ctx->rem_interval.tv_sec;
			interval_nsec = db_ctx->rem_interval.tv_nsec;
		}

		if (FD_ISSET(uevent_fd, &set)) {
			char buf[2048];
			int i, n;
			int is_subsys_block = 0, is_devname_nvme = 0;
			int is_subsys_nvme_subsys = 0, is_subsys_nvme = 0;

			while (1) {
				n = recv(uevent_fd, buf, sizeof(buf),
						MSG_DONTWAIT);
				if (n < 0) {
					if (errno == EAGAIN)
						break;

					if (errno == EINTR)
						continue;

					/*
					 * We may have missed some netlink
					 * uevents from kernel. This is not a
					 * fatal error and we may synthesize it
					 * as an NVME kobject change event and
					 * force a topology rescan.
					 */
					if (errno == ENOBUFS)
						return EVENT_TYPE_NVME_UEVENT;

					nvme_show_perror("read from uevent fd");
					return n;
				}

				for (i = 0; i < n; ) {
					char *s = &buf[i];

					if (!strncmp(s, "SUBSYSTEM=block", 15))
						is_subsys_block = 1;

					if (!strncmp(s, "DEVNAME=nvme", 12))
						is_devname_nvme = 1;

					if (!strncmp(s,
						"SUBSYSTEM=nvme-subsystem", 24))
						is_subsys_nvme_subsys = 1;

					if (!strncmp(s, "SUBSYSTEM=nvme", 14))
						is_subsys_nvme = 1;

					i += strlen(s) + 1;
				}

				if (is_subsys_block || is_subsys_nvme_subsys ||
					is_subsys_nvme || is_devname_nvme)
					return EVENT_TYPE_NVME_UEVENT;

			}
		}

		if (FD_ISSET(term_fd, &set)) {
			while (1) {
				ret = read(term_fd, c, 1);
				if (ret < 0) {
					if (errno == EINTR)
						continue;
					nvme_show_perror("read from term fd");
					return EVENT_TYPE_ERROR;
				}
				if (ret == 1)
					return EVENT_TYPE_KEY_PRESS;
			}
		}
	}
}

static enum event_type wait_for_esc_seq(struct dashboard_ctx *db_ctx)
{
	unsigned char c;
	enum event_type event;

	event = wait_for_event(db_ctx, &c, 1);
	switch (event) {
	case EVENT_TYPE_ERROR:	/* fall through */
	case EVENT_TYPE_KEY_QUIT:
		return event;
	case EVENT_TYPE_TIMEOUT:
		return EVENT_TYPE_KEY_ESC;
	default:
		if (c == 91) { /* '[' key */
			event = wait_for_event(db_ctx, &c, 1);
			switch (event) {
			case EVENT_TYPE_ERROR:		/* fall through */
			case EVENT_TYPE_KEY_QUIT:	/* fall through */
				return event;
			case EVENT_TYPE_TIMEOUT:
				/* ignore */
				break;
			default:
				if (c == 65)
					return EVENT_TYPE_KEY_UP;
				else if (c == 66)
					return EVENT_TYPE_KEY_DOWN;
				else if (c == 53 || c == 54) {
					char prev = c;

					event = wait_for_event(db_ctx, &c, 1);
					switch (event) {
					case EVENT_TYPE_ERROR:	/* fall through */
					case EVENT_TYPE_KEY_QUIT:
						return event;
					case EVENT_TYPE_TIMEOUT:
						/* ignore */
						break;
					default:
						if (c == 126 && prev == 53)
							return EVENT_TYPE_KEY_PAGE_UP;
						else if (c == 126 && prev == 54)
							return EVENT_TYPE_KEY_PAGE_DOWN;
						/* else ignore */
						break;
					}
				}
				/* else ignore */
				break;
			}
		}
	}
	return EVENT_TYPE_IGNORE;
}

enum event_type dashboard_wait_for_event(struct dashboard_ctx *db_ctx)
{
	int event;
	unsigned char c;

	db_ctx->rem_interval.tv_sec = 0;
	db_ctx->rem_interval.tv_nsec = 0;

	while (1) {
		event = wait_for_event(db_ctx, &c, 0);
		switch (event) {
		case EVENT_TYPE_ERROR:		/* fall through */
		case EVENT_TYPE_TIMEOUT:	/* fall through */
		case EVENT_TYPE_NVME_UEVENT:	/* fall through */
		case EVENT_TYPE_SIGWINCH:	/* fall through */
		case EVENT_TYPE_KEY_QUIT:
			return event;
		default:
			if (c == 27) {	/* 'ESC' key */
				/* read escape sequence */
				event = wait_for_esc_seq(db_ctx);
				if (event != EVENT_TYPE_IGNORE)
					return event;
			} else if (c == '\n' || c == '\r') {
				return EVENT_TYPE_KEY_RETURN;
			} else if (c == 'q') {
				return EVENT_TYPE_KEY_QUIT;
			} /* else ignore */
			break;
		}
	}
}

static void draw_line(int row, char *buf, bool reverse)
{
	/* move cursor to @row */
	printf("\033[%d;1H", row);

	/* clear the row */
	printf("\033[2K");

	if (reverse)
		printf("\033[7m");	/* turn on reversed video */

	if (buf) {
		/*
		 * As we move cursor to individual row and print each line,
		 * we don't need to print '\n'.
		 */
		while (*buf != '\n' && *buf != '\0')
			putchar(*buf++);
	}

	if (reverse)
		printf("\033[m");	/* turn off reversed video */
}

int dashboard_draw_frame(struct dashboard_ctx *db_ctx, int scroll)
{
	char *pos;
	int header_start_off, header_end_off;
	int footer_start_off, footer_end_off;
	int data_start_off, data_end_off, data_rows;
	int row, off, num, resrv_rows;
	int rev_header_off = -1, rev_data_off = -1, rev_footer_off = -1;
	struct data_store *ds = &db_ctx->ds;
	FILE *stream = ds->stream;
	struct win_frame *frame = &db_ctx->frame;

	/*
	 * If this is scrolling update then just re-adjust the rows in a frame
	 * otherwise we repaint the enitre frame post processing the screen
	 * buffer.
	 */
	if (!scroll) {
		/* flushing stream would synchronize screen buffer */
		fflush(stream);

		/*
		 * Rewind the stream to reset the file offset position to the
		 * start of the buffer.
		 */
		rewind(stream);

		/* If there's nothing to print then return early. */
		if (!ds->len)
			return 0;

		ds->buf[ds->len] = '\0';

		/*
		 * Parse screen buffer to find num of rows in the buffer (each
		 * row ends with new-line) and annotate each row offset. As we
		 * render the dashboard line by line we count num of lines/rows
		 * present in the data store buffer and then also calculate as
		 * well as store the start offset of each line.
		 */
		ds->num_rows = 0;
		pos = ds->buf;
		while (*pos) {
			if (*pos++ == '\n')
				ds->num_rows++;
		}

		/* If there're no lines in the buffer then return. */
		if (!ds->num_rows) {
			nvme_show_error("data buffer doesn't contain any line");
			return -EINVAL;
		}

		free(ds->row_off);

		ds->row_off = calloc(ds->num_rows, sizeof(*ds->row_off));
		if (!ds->row_off) {
			nvme_show_error("Failed to allocate row offset buffer");
			return -ENOMEM;
		}

		num = 0;
		ds->row_off[num] = 0;	/* first line starts at offset 0 */
		pos = ds->buf;
		while (*pos && num + 1 < ds->num_rows) {
			if (*pos++ == '\n')
				ds->row_off[++num] = pos - ds->buf;
		}
	}

	/*
	 * Calculate the number of rows that can be displayed in a single
	 * screen frame. Printing more rows than could fit on the one screen
	 * causes the terminal to scroll, leading to noticeable flicker and a
	 * cluttered dashboard display.
	 * We draw the dashboard data including header and footer. We know
	 * the current window size and hence we reserved rows for header and
	 * footer first. Then whatever num of rows are remaining is used to
	 * draw the data.
	 */
	resrv_rows = ds->header_rows + ds->footer_rows;
	frame->data_rows = frame->rows - resrv_rows;

	/*
	 * If the current window size is less than num of reserved rows
	 * (i.e. header + footer) then we can't draw frame. In such case
	 * return without drawig anything.
	 */
	if (frame->data_rows < 0)
		return 0;

	frame->header_start_off = header_start_off = 0;
	header_end_off = header_start_off + ds->header_rows;

	/* total num of data rows present in the current screen buffer */
	ds->data_rows = ds->num_rows - resrv_rows;

	/*
	 * Num of data rows which should be printed starting at index
	 * @ds->data_start_idx.
	 */
	data_rows = ds->data_rows - ds->data_start_idx;

	/*
	 * Calculate data rows which could be actually accomodated in the
	 * current frame. If @data_rows is greater than @frame->data_rows
	 * then we clamp it to frame->data_row.
	 */
	data_rows = min(data_rows, frame->data_rows);
	data_start_off = ds->header_rows + ds->data_start_idx;
	data_end_off = data_start_off + data_rows;

	frame->data_start_off = frame->header_start_off + ds->header_rows;

	frame->footer_start_off = frame->data_start_off + frame->data_rows;
	footer_start_off = ds->header_rows + ds->data_rows;
	footer_end_off = footer_start_off + ds->footer_rows;


	 /* print header */
	if (ds->rev_header_row >= 0)
		rev_header_off = ds->rev_header_row;

	for (off = header_start_off, row = frame->header_start_off + 1;
			off < header_end_off; off++, row++)
		draw_line(row, ds->buf + ds->row_off[off],
				off == rev_header_off);

	/* print data */
	if (ds->rev_data_row >= 0)
		rev_data_off = ds->header_rows + ds->rev_data_row;

	for (off = data_start_off, row = frame->data_start_off + 1;
			off < data_end_off; off++, row++)
		draw_line(row, ds->buf + ds->row_off[off],
				off == rev_data_off);

	/*
	 * Clear remaining data rows, if any. If @data_rows is less than the
	 * @frame->data_rows then we would have some empty rows at the end of
	 * data and we have to clear it off.
	 */
	if (data_rows < frame->data_rows) {
		int last_data_row = ds->header_rows + frame->data_rows;

		for (row = frame->data_start_off + data_rows + 1;
				row <= last_data_row; row++)
			draw_line(row, NULL, false);
	}

	/* print footer */
	if (ds->rev_footer_row >= 0)
		rev_footer_off = ds->header_rows + ds->data_rows +
					ds->rev_footer_row;

	for (off = footer_start_off, row = frame->footer_start_off + 1;
			off < footer_end_off; off++, row++)
		draw_line(row, ds->buf + ds->row_off[off],
				off == rev_footer_off);

	fflush(stdout);

	return 0;
}

void dashboard_reset(struct dashboard_ctx *db_ctx)
{
	dashboard_set_header_rows(db_ctx, 0);
	dashboard_set_data_start(db_ctx, 0);
	dashboard_set_footer_rows(db_ctx, 0);

	dashboard_reset_data_row_reverse(db_ctx);
	dashboard_reset_header_row_reverse(db_ctx);
	dashboard_reset_footer_row_reverse(db_ctx);

	fflush(db_ctx->ds.stream);

	/* clear screen */
	printf("\033[2J");
}

static int dashboard_uevent_fd(void)
{
	int fd, ret;
	struct sockaddr_nl sa;

	fd = socket(AF_NETLINK, SOCK_DGRAM, NETLINK_KOBJECT_UEVENT);
	if (fd < 0) {
		nvme_show_perror("uevent socket");
		return -errno;
	}

	sa.nl_family = AF_NETLINK;
	sa.nl_pad = 0;
	sa.nl_pid = getpid();
	sa.nl_groups = 1;

	ret = bind(fd, (struct sockaddr *)&sa, sizeof(struct sockaddr_nl));
	if (ret < 0) {
		close(fd);
		nvme_show_perror("uevent bind");
		return -errno;
	}

	return fd;
}

FILE *dashboard_init(struct dashboard_ctx **db_ctx, int refresh_interval)
{
	sigset_t sigwinch_set;
	struct termios ts;
	struct winsize ws;
	struct data_store *ds;
	struct dashboard_ctx *ctx;

	ctx = malloc(sizeof(struct dashboard_ctx));
	if (!ctx)
		return NULL;
	memset(ctx, 0, sizeof(struct dashboard_ctx));

	ctx->interval = refresh_interval;

	ctx->term_fd = open(ctermid(NULL), O_RDWR);
	if (ctx->term_fd < 0) {
		free(ctx);
		nvme_show_perror("open controlling terminal");
		return NULL;
	}

	/*
	 * listen for kobject uevent
	 */
	ctx->uevent_fd = dashboard_uevent_fd();
	if (ctx->uevent_fd < 0)
		goto out_term_fd;

	/*
	 * First block SIGWINCH and note down the current window size; we'd
	 * later atomically unblock SIGWINCH and wait for both user input and
	 * window size change events using pselect(). This ensures that we don't
	 * miss window size change events.
	 */
	sigemptyset(&sigwinch_set);
	sigemptyset(&ctx->orig_set);
	sigaddset(&sigwinch_set, SIGWINCH);
	/* block SIGWINCH */
	sigprocmask(SIG_BLOCK, &sigwinch_set, &ctx->orig_set);
	/* get current value of window size */
	if (ioctl(ctx->term_fd, TIOCGWINSZ, &ws) < 0) {
		nvme_show_perror("ioctl TIOCGWINSZ");
		goto out_reset_mask;
	}

	ctx->frame.rows = ws.ws_row;

	/* put terminal in raw mode */
	if (tty_set_raw(ctx->term_fd, &ts) < 0) {
		nvme_show_error("Failed to set tty in raw mode");
		goto out_reset_mask;
	}
	ctx->orig_ts = ts;

	ds = &ctx->ds;
	ds->stream = open_memstream(&ds->buf, &ds->len);
	if (!ds->stream) {
		nvme_show_perror("open memstream");
		goto out_reset_tty;
	}
	ds->rev_data_row = ds->rev_header_row = ds->rev_footer_row = -1;

	/* hide cursor */
	printf("\033[?25l");

	/* clear screen */
	printf("\033[2J");
	fflush(stdout);

	*db_ctx = ctx;
	return ds->stream;
out_reset_tty:
	/* reset terminal */
	tty_reset(ctx->term_fd, &ctx->orig_ts);
out_reset_mask:
	/* restore the original signal mask */
	sigprocmask(SIG_SETMASK, &ctx->orig_set, NULL);
	close(ctx->uevent_fd);
out_term_fd:
	close(ctx->term_fd);
	free(ctx);
	return NULL;
}

void dashboard_exit(struct dashboard_ctx *db_ctx)
{
	struct data_store *ds = &db_ctx->ds;

	/* show cursor */
	printf("\033[?25h\n");
	fflush(stdout);

	fclose(ds->stream);
	free(ds->buf);
	free(ds->row_off);

	/* reset terminal */
	tty_reset(db_ctx->term_fd, &db_ctx->orig_ts);

	/* restore the original signal mask */
	sigprocmask(SIG_SETMASK, &db_ctx->orig_set, NULL);
	close(db_ctx->term_fd);
	close(db_ctx->uevent_fd);
	free(db_ctx);
}