From: Karl Beldan <karl.beldan@xxxxxxxxxxxxxxxx> Helps feel current minstrel and stack rate-control API limits. Helped trigger some bugs in vht tx code path in the past. Some ppl were interested in checking that out. some TODOs: - Optimize rate-indexes loops and sampling holes - The txinfo flags for vht STAs VHT rates support depends on a new CONFIG_MAC80211_RC_MINSTREL_VHT. Signed-off-by: Karl Beldan <karl.beldan@xxxxxxxxxxxxxxxx> --- net/mac80211/Kconfig | 7 + net/mac80211/rc80211_minstrel_ht.c | 235 ++++++++++++++++++++++++----- net/mac80211/rc80211_minstrel_ht.h | 33 +++- net/mac80211/rc80211_minstrel_ht_debugfs.c | 30 ++-- 4 files changed, 248 insertions(+), 57 deletions(-) diff --git a/net/mac80211/Kconfig b/net/mac80211/Kconfig index 62535fe..190b59e 100644 --- a/net/mac80211/Kconfig +++ b/net/mac80211/Kconfig @@ -40,6 +40,13 @@ config MAC80211_RC_MINSTREL_HT ---help--- This option enables the 'minstrel_ht' TX rate control algorithm +config MAC80211_RC_MINSTREL_VHT + bool "Minstrel 802.11vht support" if EXPERT + depends on MAC80211_RC_MINSTREL_HT + default n + ---help--- + This option enables vht in the 'minstrel_ht' TX rate control algorithm + choice prompt "Default rate control algorithm" depends on MAC80211_HAS_RC diff --git a/net/mac80211/rc80211_minstrel_ht.c b/net/mac80211/rc80211_minstrel_ht.c index 84ae70b..dd81516 100644 --- a/net/mac80211/rc80211_minstrel_ht.c +++ b/net/mac80211/rc80211_minstrel_ht.c @@ -18,6 +18,10 @@ #define AVG_PKT_SIZE 1200 +#define BW_20 0 +#define BW_40 1 +#define BW_80 2 + /* Number of bits for an average sized packet */ #define MCS_NBITS (AVG_PKT_SIZE << 3) @@ -38,8 +42,9 @@ * Define group sort order: HT40 -> SGI -> #streams */ #define GROUP_IDX(_streams, _sgi, _ht40) \ - MINSTREL_MAX_STREAMS * 2 * _ht40 + \ - MINSTREL_MAX_STREAMS * _sgi + \ + MINSTREL_HT_GROUP_0 + \ + MINSTREL_HT_MAX_STREAMS * 2 * _ht40 + \ + MINSTREL_HT_MAX_STREAMS * _sgi + \ _streams - 1 /* MCS rate information for an MCS group */ @@ -61,6 +66,37 @@ } \ } +#define VHT_GROUP_IDX(_streams, _sgi, _bw) \ + (MINSTREL_VHT_GROUP_0 + \ + MINSTREL_VHT_MAX_STREAMS * 2 * (_bw) + \ + MINSTREL_VHT_MAX_STREAMS * (_sgi) + \ + (_streams) - 1) + +#define BW2VBPS(_bw, r3, r2, r1) \ + (_bw == BW_80 ? r3 : _bw == BW_40 ? r2 : r1) + +#define VHT_GROUP(_streams, _sgi, _bw) \ + [VHT_GROUP_IDX(_streams, _sgi, _bw)] = { \ + .streams = _streams, \ + .flags = \ + (_sgi ? IEEE80211_TX_RC_SHORT_GI : 0) | \ + (_bw == BW_80 ? IEEE80211_TX_RC_80_MHZ_WIDTH : \ + _bw == BW_40 ? IEEE80211_TX_RC_40_MHZ_WIDTH : 0), \ + .duration = { \ + MCS_DURATION(_streams, _sgi, BW2VBPS(_bw, 117, 54, 26)), \ + MCS_DURATION(_streams, _sgi, BW2VBPS(_bw, 234, 108, 52)), \ + MCS_DURATION(_streams, _sgi, BW2VBPS(_bw, 351, 162, 78)), \ + MCS_DURATION(_streams, _sgi, BW2VBPS(_bw, 468, 216, 104)), \ + MCS_DURATION(_streams, _sgi, BW2VBPS(_bw, 702, 324, 156)), \ + MCS_DURATION(_streams, _sgi, BW2VBPS(_bw, 936, 432, 208)), \ + MCS_DURATION(_streams, _sgi, BW2VBPS(_bw, 1053, 486, 234)), \ + MCS_DURATION(_streams, _sgi, BW2VBPS(_bw, 1170, 540, 260)), \ + MCS_DURATION(_streams, _sgi, BW2VBPS(_bw, 1404, 648, 312)), \ + MCS_DURATION(_streams, _sgi, BW2VBPS(_bw, 1560, 720, 346)) \ + } \ +} + + #define CCK_DURATION(_bitrate, _short, _len) \ (1000 * (10 /* SIFS */ + \ (_short ? 72 + 24 : 144 + 48 ) + \ @@ -76,13 +112,13 @@ CCK_ACK_DURATION(55, _short), \ CCK_ACK_DURATION(110, _short) -#define CCK_GROUP \ - [MINSTREL_MAX_STREAMS * MINSTREL_STREAM_GROUPS] = { \ - .streams = 0, \ - .duration = { \ - CCK_DURATION_LIST(false), \ - CCK_DURATION_LIST(true) \ - } \ +#define CCK_GROUP \ + [MINSTREL_CCK_GROUP] = { \ + .streams = 0, \ + .duration = { \ + CCK_DURATION_LIST(false), \ + CCK_DURATION_LIST(true) \ + } \ } /* @@ -91,38 +127,56 @@ * use. * * Sortorder has to be fixed for GROUP_IDX macro to be applicable: - * HT40 -> SGI -> #streams + * BW -> SGI -> #streams */ const struct mcs_group minstrel_mcs_groups[] = { - MCS_GROUP(1, 0, 0), - MCS_GROUP(2, 0, 0), -#if MINSTREL_MAX_STREAMS >= 3 - MCS_GROUP(3, 0, 0), + MCS_GROUP(1, 0, BW_20), + MCS_GROUP(2, 0, BW_20), +#if MINSTREL_HT_MAX_STREAMS >= 3 + MCS_GROUP(3, 0, BW_20), #endif - MCS_GROUP(1, 1, 0), - MCS_GROUP(2, 1, 0), -#if MINSTREL_MAX_STREAMS >= 3 - MCS_GROUP(3, 1, 0), + MCS_GROUP(1, 1, BW_20), + MCS_GROUP(2, 1, BW_20), +#if MINSTREL_HT_MAX_STREAMS >= 3 + MCS_GROUP(3, 1, BW_20), #endif - MCS_GROUP(1, 0, 1), - MCS_GROUP(2, 0, 1), -#if MINSTREL_MAX_STREAMS >= 3 - MCS_GROUP(3, 0, 1), + MCS_GROUP(1, 0, BW_40), + MCS_GROUP(2, 0, BW_40), +#if MINSTREL_HT_MAX_STREAMS >= 3 + MCS_GROUP(3, 0, BW_40), #endif - MCS_GROUP(1, 1, 1), - MCS_GROUP(2, 1, 1), -#if MINSTREL_MAX_STREAMS >= 3 - MCS_GROUP(3, 1, 1), + MCS_GROUP(1, 1, BW_40), + MCS_GROUP(2, 1, BW_40), +#if MINSTREL_HT_MAX_STREAMS >= 3 + MCS_GROUP(3, 1, BW_40), #endif + CCK_GROUP, + /* must be last */ - CCK_GROUP -}; +#ifdef CONFIG_MAC80211_RC_MINSTREL_VHT + VHT_GROUP(1, 0, BW_20), + VHT_GROUP(2, 0, BW_20), -#define MINSTREL_CCK_GROUP (ARRAY_SIZE(minstrel_mcs_groups) - 1) + VHT_GROUP(1, 1, BW_20), + VHT_GROUP(2, 1, BW_20), + + VHT_GROUP(1, 0, BW_40), + VHT_GROUP(2, 0, BW_40), + + VHT_GROUP(1, 1, BW_40), + VHT_GROUP(2, 1, BW_40), + + VHT_GROUP(1, 0, BW_80), + VHT_GROUP(2, 0, BW_80), + + VHT_GROUP(1, 1, BW_80), + VHT_GROUP(2, 1, BW_80) +#endif +}; static u8 sample_table[SAMPLE_COLUMNS][MCS_GROUP_RATES]; @@ -130,6 +184,44 @@ static void minstrel_ht_update_rates(struct minstrel_priv *mp, struct minstrel_ht_sta *mi); /* + * Some VHT MCSes are invalid (when Nes does not divide Ndbps) + * e.g for MCS9@20MHzx1Nss: Ndbps=8x52*(3/4) Nes=1 + * + * Returns the valid mcs map for struct minstrel_mcs_group_data.supported + */ +static u16 +minstrel_get_valid_vht_rates(int bw, int nss, u16 mcs_map) +{ + u16 mask = 0; + + if (bw == BW_20) { + if (nss != 3 && nss != 6) + mask = BIT(9); + } else if (bw == BW_80) { + if (nss == 3 || nss == 7) + mask = BIT(6); + else if (nss == 6) + mask = BIT(9); + } else + WARN_ON(bw != BW_40); + + switch ((le16_to_cpu(mcs_map) >> (2 * (nss - 1))) & 3) { + case IEEE80211_VHT_MCS_SUPPORT_0_7: + mask |= 0x300; + break; + case IEEE80211_VHT_MCS_SUPPORT_0_8: + mask |= 0x200; + break; + case IEEE80211_VHT_MCS_SUPPORT_0_9: + break; + default: + mask = 0x3ff; + } + + return 0x3ff & ~mask; +} + +/* * Look up an MCS group index based on mac80211 rate information */ static int @@ -140,6 +232,15 @@ minstrel_ht_get_group_idx(struct ieee80211_tx_rate *rate) !!(rate->flags & IEEE80211_TX_RC_40_MHZ_WIDTH)); } +static int +minstrel_vht_get_group_idx(struct ieee80211_tx_rate *rate) +{ + return VHT_GROUP_IDX(ieee80211_rate_get_vht_nss(rate), + !!(rate->flags & IEEE80211_TX_RC_SHORT_GI), + !!(rate->flags & IEEE80211_TX_RC_40_MHZ_WIDTH) + + 2*!!(rate->flags & IEEE80211_TX_RC_80_MHZ_WIDTH)); +} + static struct minstrel_rate_stats * minstrel_ht_get_stats(struct minstrel_priv *mp, struct minstrel_ht_sta *mi, struct ieee80211_tx_rate *rate) @@ -149,6 +250,9 @@ minstrel_ht_get_stats(struct minstrel_priv *mp, struct minstrel_ht_sta *mi, if (rate->flags & IEEE80211_TX_RC_MCS) { group = minstrel_ht_get_group_idx(rate); idx = rate->idx % 8; + } else if (rate->flags & IEEE80211_TX_RC_VHT_MCS) { + group = minstrel_vht_get_group_idx(rate); + idx = ieee80211_rate_get_vht_mcs(rate); } else { group = MINSTREL_CCK_GROUP; @@ -386,7 +490,8 @@ minstrel_ht_txstat_valid(struct minstrel_priv *mp, struct ieee80211_tx_rate *rat if (!rate->count) return false; - if (rate->flags & IEEE80211_TX_RC_MCS) + if (rate->flags & IEEE80211_TX_RC_MCS || + rate->flags & IEEE80211_TX_RC_VHT_MCS) return true; return rate->idx == mp->cck_rates[0] || @@ -635,6 +740,10 @@ minstrel_ht_set_rate(struct minstrel_priv *mp, struct minstrel_ht_sta *mi, if (index / MCS_GROUP_RATES == MINSTREL_CCK_GROUP) { idx = mp->cck_rates[index % ARRAY_SIZE(mp->cck_rates)]; flags = 0; + } else if (index / MCS_GROUP_RATES >= MINSTREL_VHT_GROUP_0) { + idx = ((group->streams - 1) << 4) | + ((index % MCS_GROUP_RATES) & ~0xF); + flags = IEEE80211_TX_RC_VHT_MCS | group->flags; } else { idx = index % MCS_GROUP_RATES + (group->streams - 1) * 8; flags = IEEE80211_TX_RC_MCS | group->flags; @@ -817,6 +926,11 @@ minstrel_ht_get_rate(void *priv, struct ieee80211_sta *sta, void *priv_sta, rate->idx = mp->cck_rates[idx]; rate->flags = 0; return; + } else if (sample_idx / MCS_GROUP_RATES >= MINSTREL_VHT_GROUP_0) { + rate->flags = IEEE80211_TX_RC_VHT_MCS | sample_group->flags; + ieee80211_rate_set_vht(rate, sample_idx % MCS_GROUP_RATES, + sample_group->streams); + return; } rate->idx = sample_idx % MCS_GROUP_RATES + @@ -861,6 +975,8 @@ minstrel_ht_update_caps(void *priv, struct ieee80211_supported_band *sband, struct minstrel_ht_sta *mi = &msp->ht; struct ieee80211_mcs_info *mcs = &sta->ht_cap.mcs; u16 sta_cap = sta->ht_cap.cap; + struct ieee80211_sta_vht_cap *vht_cap = &sta->vht_cap; + int vht_only; int n_supported = 0; int ack_dur; int stbc; @@ -870,8 +986,10 @@ minstrel_ht_update_caps(void *priv, struct ieee80211_supported_band *sband, if (!sta->ht_cap.ht_supported) goto use_legacy; - BUILD_BUG_ON(ARRAY_SIZE(minstrel_mcs_groups) != - MINSTREL_MAX_STREAMS * MINSTREL_STREAM_GROUPS + 1); + BUILD_BUG_ON(ARRAY_SIZE(minstrel_mcs_groups) != MINSTREL_GROUPS_NB); + + /* For the moment be less verbose and disable ht rates for a vht sta */ + vht_only = vht_cap->vht_supported; msp->is_ht = true; memset(mi, 0, sizeof(*mi)); @@ -896,22 +1014,32 @@ minstrel_ht_update_caps(void *priv, struct ieee80211_supported_band *sband, } mi->sample_tries = 4; - stbc = (sta_cap & IEEE80211_HT_CAP_RX_STBC) >> - IEEE80211_HT_CAP_RX_STBC_SHIFT; - mi->tx_flags |= stbc << IEEE80211_TX_CTL_STBC_SHIFT; + /* TODO tx_flags for vht - ATM the RC API is not fine-grained enough */ + if (!vht_only) { + stbc = (sta_cap & IEEE80211_HT_CAP_RX_STBC) >> + IEEE80211_HT_CAP_RX_STBC_SHIFT; + mi->tx_flags |= stbc << IEEE80211_TX_CTL_STBC_SHIFT; + } if (sta_cap & IEEE80211_HT_CAP_LDPC_CODING) mi->tx_flags |= IEEE80211_TX_CTL_LDPC; for (i = 0; i < ARRAY_SIZE(mi->groups); i++) { + u32 gflags = minstrel_mcs_groups[i].flags; + mi->groups[i].supported = 0; if (i == MINSTREL_CCK_GROUP) { minstrel_ht_update_cck(mp, mi, sband, sta); continue; } - if (minstrel_mcs_groups[i].flags & IEEE80211_TX_RC_SHORT_GI) { - if (minstrel_mcs_groups[i].flags & IEEE80211_TX_RC_40_MHZ_WIDTH) { +#ifdef CONFIG_MAC80211_RC_MINSTREL_VHT /* FIXME otherwise MINSTREL_VHT_GROUP_0 is 0 */ + if (vht_only && i < MINSTREL_VHT_GROUP_0) + continue; +#endif + + if (gflags & IEEE80211_TX_RC_SHORT_GI) { + if (gflags & IEEE80211_TX_RC_40_MHZ_WIDTH) { if (!(sta_cap & IEEE80211_HT_CAP_SGI_40)) continue; } else { @@ -920,7 +1048,7 @@ minstrel_ht_update_caps(void *priv, struct ieee80211_supported_band *sband, } } - if (minstrel_mcs_groups[i].flags & IEEE80211_TX_RC_40_MHZ_WIDTH && + if (gflags & IEEE80211_TX_RC_40_MHZ_WIDTH && sta->bandwidth < IEEE80211_STA_RX_BW_40) continue; @@ -929,8 +1057,35 @@ minstrel_ht_update_caps(void *priv, struct ieee80211_supported_band *sband, minstrel_mcs_groups[i].streams > 1) continue; - mi->groups[i].supported = - mcs->rx_mask[minstrel_mcs_groups[i].streams - 1]; + if (i >= MINSTREL_VHT_GROUP_0) { + int bw; + if (!vht_cap->vht_supported) + continue; + if (gflags & IEEE80211_TX_RC_80_MHZ_WIDTH) { + + if (sta->bandwidth < IEEE80211_STA_RX_BW_80 || + ((gflags & IEEE80211_TX_RC_SHORT_GI) && + !(vht_cap->cap & IEEE80211_VHT_CAP_SHORT_GI_80))) { + continue; + } + } + if (WARN_ON(gflags & IEEE80211_TX_RC_160_MHZ_WIDTH)) + continue; + + if (gflags & IEEE80211_TX_RC_40_MHZ_WIDTH) + bw = BW_40; + else if (gflags & IEEE80211_TX_RC_80_MHZ_WIDTH) + bw = BW_80; + else + bw = BW_20; + mi->groups[i].supported = + minstrel_get_valid_vht_rates(bw, + minstrel_mcs_groups[i].streams, + vht_cap->vht_mcs.tx_mcs_map); + } else { + mi->groups[i].supported = + mcs->rx_mask[minstrel_mcs_groups[i].streams - 1]; + } if (mi->groups[i].supported) n_supported++; diff --git a/net/mac80211/rc80211_minstrel_ht.h b/net/mac80211/rc80211_minstrel_ht.h index d655586..71f5a13 100644 --- a/net/mac80211/rc80211_minstrel_ht.h +++ b/net/mac80211/rc80211_minstrel_ht.h @@ -13,10 +13,33 @@ * The number of streams can be changed to 2 to reduce code * size and memory footprint. */ -#define MINSTREL_MAX_STREAMS 3 -#define MINSTREL_STREAM_GROUPS 4 +#ifdef CONFIG_MAC80211_RC_MINSTREL_VHT +#define MINSTREL_VHT_MAX_STREAMS 2 +#else +#define MINSTREL_VHT_MAX_STREAMS 0 +#endif +#define MINSTREL_VHT_STREAM_GROUPS 6 /* BW(=3)*SGI(=2)*/ + +#define MINSTREL_HT_MAX_STREAMS 3 +#define MINSTREL_HT_STREAM_GROUPS 4 + -#define MCS_GROUP_RATES 8 +#define MINSTREL_HT_GROUPS_NB (MINSTREL_HT_MAX_STREAMS * MINSTREL_HT_STREAM_GROUPS) +#define MINSTREL_VHT_GROUPS_NB (MINSTREL_VHT_MAX_STREAMS * MINSTREL_VHT_STREAM_GROUPS) +#define MINSTREL_CCK_GROUPS_NB 1 +#define MINSTREL_GROUPS_NB (MINSTREL_HT_GROUPS_NB + \ + MINSTREL_VHT_GROUPS_NB + \ + MINSTREL_CCK_GROUPS_NB) + +#define MINSTREL_HT_GROUP_0 0 +#define MINSTREL_CCK_GROUP (MINSTREL_HT_GROUP_0 + MINSTREL_HT_GROUPS_NB) +#define MINSTREL_VHT_GROUP_0 (MINSTREL_CCK_GROUP + 1) + +#ifdef CONFIG_MAC80211_RC_MINSTREL_VHT +#define MCS_GROUP_RATES 10 +#else +#define MCS_GROUP_RATES 8 +#endif struct mcs_group { u32 flags; @@ -53,7 +76,7 @@ struct minstrel_mcs_group_data { u8 column; /* bitfield of supported MCS rates of this group */ - u8 supported; + u16 supported; /* selected primary rates */ unsigned int max_tp_rate; @@ -109,7 +132,7 @@ struct minstrel_ht_sta { u8 cck_supported_short; /* MCS rate group info and statistics */ - struct minstrel_mcs_group_data groups[MINSTREL_MAX_STREAMS * MINSTREL_STREAM_GROUPS + 1]; + struct minstrel_mcs_group_data groups[MINSTREL_GROUPS_NB]; }; struct minstrel_ht_sta_priv { diff --git a/net/mac80211/rc80211_minstrel_ht_debugfs.c b/net/mac80211/rc80211_minstrel_ht_debugfs.c index 3e7d793..cac3ada 100644 --- a/net/mac80211/rc80211_minstrel_ht_debugfs.c +++ b/net/mac80211/rc80211_minstrel_ht_debugfs.c @@ -18,7 +18,6 @@ static char * minstrel_ht_stats_dump(struct minstrel_ht_sta *mi, int i, char *p) { - unsigned int max_mcs = MINSTREL_MAX_STREAMS * MINSTREL_STREAM_GROUPS; const struct mcs_group *mg; unsigned int j, tp, prob, eprob; char htmode = '2'; @@ -30,6 +29,8 @@ minstrel_ht_stats_dump(struct minstrel_ht_sta *mi, int i, char *p) mg = &minstrel_mcs_groups[i]; if (mg->flags & IEEE80211_TX_RC_40_MHZ_WIDTH) htmode = '4'; + else if (mg->flags & IEEE80211_TX_RC_80_MHZ_WIDTH) + htmode = '8'; if (mg->flags & IEEE80211_TX_RC_SHORT_GI) gimode = 'S'; @@ -41,27 +42,31 @@ minstrel_ht_stats_dump(struct minstrel_ht_sta *mi, int i, char *p) if (!(mi->groups[i].supported & BIT(j))) continue; - if (i == max_mcs) - p += sprintf(p, "CCK/%cP ", j < 4 ? 'L' : 'S'); + if (i == MINSTREL_CCK_GROUP) + p += sprintf(p, " CCK/%cP ", j < 4 ? 'L' : 'S'); + else if (i >= MINSTREL_VHT_GROUP_0) + p += sprintf(p, "VHT%c0/%cGI ", htmode, gimode); else - p += sprintf(p, "HT%c0/%cGI ", htmode, gimode); + p += sprintf(p, " HT%c0/%cGI ", htmode, gimode); *(p++) = (idx == mi->max_tp_rate) ? 'T' : ' '; *(p++) = (idx == mi->max_tp_rate2) ? 't' : ' '; *(p++) = (idx == mi->max_prob_rate) ? 'P' : ' '; - if (i == max_mcs) { + if (i == MINSTREL_CCK_GROUP) { int r = bitrates[j % 4]; - p += sprintf(p, " %2u.%1uM", r / 10, r % 10); + p += sprintf(p, " %2u.%1uM ", r / 10, r % 10); + } else if (i >= MINSTREL_VHT_GROUP_0) { + p += sprintf(p, " MCS%-2u %1u", j, mg->streams); } else { - p += sprintf(p, " MCS%-2u", (mg->streams - 1) * 8 + j); + p += sprintf(p, " MCS%-2u ", (mg->streams - 1) * 8 + j); } tp = mr->cur_tp / 10; prob = MINSTREL_TRUNC(mr->cur_prob * 1000); eprob = MINSTREL_TRUNC(mr->probability * 1000); - p += sprintf(p, " %6u.%1u %6u.%1u %6u.%1u " + p += sprintf(p, " %6u.%1u %6u.%1u %6u.%1u " "%3u %3u(%3u) %8llu %8llu\n", tp / 10, tp % 10, eprob / 10, eprob % 10, @@ -83,7 +88,6 @@ minstrel_ht_stats_open(struct inode *inode, struct file *file) struct minstrel_ht_sta *mi = &msp->ht; struct minstrel_debugfs_info *ms; unsigned int i; - unsigned int max_mcs = MINSTREL_MAX_STREAMS * MINSTREL_STREAM_GROUPS; char *p; int ret; @@ -100,11 +104,13 @@ minstrel_ht_stats_open(struct inode *inode, struct file *file) file->private_data = ms; p = ms->buf; - p += sprintf(p, "type rate throughput ewma prob this prob " + p += sprintf(p, " type rate nss throughput ewma prob this prob " "retry this succ/attempt success attempts\n"); - p = minstrel_ht_stats_dump(mi, max_mcs, p); - for (i = 0; i < max_mcs; i++) + p = minstrel_ht_stats_dump(mi, MINSTREL_CCK_GROUP, p); + for (i = 0; i < MINSTREL_CCK_GROUP; i++) + p = minstrel_ht_stats_dump(mi, i, p); + for (i++; i < ARRAY_SIZE(mi->groups); i++) p = minstrel_ht_stats_dump(mi, i, p); p += sprintf(p, "\nTotal packet count:: ideal %d " -- 1.8.2 -- To unsubscribe from this list: send the line "unsubscribe linux-wireless" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html