On Fri, Mar 11, 2016 at 09:51:03PM -0500, Stefan Berger wrote: > This patch implements a proxy driver for supporting multiple emulated TPMs > in a system. > > The driver implements a device /dev/vtpmx that is used to created > a client device pair /dev/tpmX (e.g., /dev/tpm10) and a server side that > is accessed using a file descriptor returned by an ioctl. > The device /dev/tpmX is the usual TPM device created by the core TPM > driver. Applications or kernel subsystems can send TPM commands to it > and the corresponding server-side file descriptor receives these > commands and delivers them to an emulated TPM. With my test script [1] running on QEMU and TPM 2.0 simulator running on the host side I get this: $ python tpm2-simulator-vtpm --host=10.0.2.2 cmd 80 01 00 00 00 0c 00 00 01 44 00 00 rsp 80 01 00 00 00 0a 00 00 00 00 Traceback (most recent call last): File "tpm2-simulator-vtpm", line 85, in <module> main() File "tpm2-simulator-vtpm", line 80, in main resp = client.send_cmd(stream) File "/home/tpmdd/tpm2-scripts/tpm2.py", line 454, in send_cmd rsp = self.simulator.send_cmd(cmd) File "/home/tpmdd/tpm2-scripts/tpm2.py", line 436, in send_cmd raise SimulatorError("Empty response") tpm2.SimulatorError: Empty response However, the process does not exit before the read call expires: $ python tpm2-list-handles Traceback (most recent call last): File "tpm2-list-handles", line 61, in <module> main() File "tpm2-list-handles", line 51, in main handles += client.get_cap(tpm2.TPM2_CAP_HANDLES, tpm2.HR_LOADED_SESSION) File "/home/tpmdd/tpm2-scripts/tpm2.py", line 782, in get_cap next_handles, more_data = self.__get_cap_cnt(cap, pt, 1) File "/home/tpmdd/tpm2-scripts/tpm2.py", line 766, in __get_cap_cnt rsp = self.send_cmd(cmd)[10:] File "/home/tpmdd/tpm2-scripts/tpm2.py", line 458, in send_cmd rsp = f.read() IOError: [Errno 62] Timer expired The server side stays stuck unti this happens. [1] git://git.infradead.org/users/jjs/tpm2-scripts.git /Jarkko > Signed-off-by: Stefan Berger <stefanb@xxxxxxxxxxxxxxxxxx> > CC: linux-kernel@xxxxxxxxxxxxxxx > CC: linux-doc@xxxxxxxxxxxxxxx > CC: linux-api@xxxxxxxxxxxxxxx > --- > drivers/char/tpm/Kconfig | 10 + > drivers/char/tpm/Makefile | 1 + > drivers/char/tpm/tpm_vtpm_proxy.c | 567 ++++++++++++++++++++++++++++++++++++++ > include/uapi/linux/Kbuild | 1 + > include/uapi/linux/vtpm_proxy.h | 42 +++ > 5 files changed, 621 insertions(+) > create mode 100644 drivers/char/tpm/tpm_vtpm_proxy.c > create mode 100644 include/uapi/linux/vtpm_proxy.h > > diff --git a/drivers/char/tpm/Kconfig b/drivers/char/tpm/Kconfig > index 3b84a8b..0eac596 100644 > --- a/drivers/char/tpm/Kconfig > +++ b/drivers/char/tpm/Kconfig > @@ -122,5 +122,15 @@ config TCG_CRB > from within Linux. To compile this driver as a module, choose > M here; the module will be called tpm_crb. > > +config TCG_VTPM_PROXY > + tristate "VTPM Proxy Interface" > + depends on TCG_TPM > + ---help--- > + This driver proxies for an emulated TPM (vTPM) running in userspace. > + A device /dev/vtpmx is provided that creates a device pair > + /dev/vtpmX and a server-side file descriptor on which the vTPM > + can receive commands. > + > + > source "drivers/char/tpm/st33zp24/Kconfig" > endif # TCG_TPM > diff --git a/drivers/char/tpm/Makefile b/drivers/char/tpm/Makefile > index 56e8f1f..98de5e6 100644 > --- a/drivers/char/tpm/Makefile > +++ b/drivers/char/tpm/Makefile > @@ -23,3 +23,4 @@ obj-$(CONFIG_TCG_IBMVTPM) += tpm_ibmvtpm.o > obj-$(CONFIG_TCG_TIS_ST33ZP24) += st33zp24/ > obj-$(CONFIG_TCG_XEN) += xen-tpmfront.o > obj-$(CONFIG_TCG_CRB) += tpm_crb.o > +obj-$(CONFIG_TCG_VTPM_PROXY) += tpm_vtpm_proxy.o > diff --git a/drivers/char/tpm/tpm_vtpm_proxy.c b/drivers/char/tpm/tpm_vtpm_proxy.c > new file mode 100644 > index 0000000..d73944e > --- /dev/null > +++ b/drivers/char/tpm/tpm_vtpm_proxy.c > @@ -0,0 +1,567 @@ > +/* > + * Copyright (C) 2015, 2016 IBM Corporation > + * > + * Author: Stefan Berger <stefanb@xxxxxxxxxx> > + * > + * Maintained by: <tpmdd-devel@xxxxxxxxxxxxxxxxxxxxx> > + * > + * Device driver for vTPM (vTPM proxy driver) > + * > + * 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, version 2 of the > + * License. > + * > + */ > + > +#include <linux/types.h> > +#include <linux/spinlock.h> > +#include <linux/uaccess.h> > +#include <linux/wait.h> > +#include <linux/miscdevice.h> > +#include <linux/vtpm_proxy.h> > +#include <linux/file.h> > +#include <linux/anon_inodes.h> > +#include <linux/poll.h> > +#include <linux/compat.h> > + > +#include "tpm.h" > + > +#define VTPM_PROXY_REQ_COMPLETE_FLAG BIT(0) > + > +struct proxy_dev { > + struct tpm_chip *chip; > + > + u32 flags; /* public API flags */ > + > + wait_queue_head_t wq; > + > + struct mutex buf_lock; /* protect buffer and flags */ > + > + long state; /* internal state */ > +#define STATE_OPENED_FLAG BIT(0) > +#define STATE_WAIT_RESPONSE_FLAG BIT(1) /* waiting for emulator response */ > + > + size_t req_len; /* length of queued TPM request */ > + size_t resp_len; /* length of queued TPM response */ > + u8 buffer[TPM_BUFSIZE]; /* request/response buffer */ > +}; > + > + > +static void vtpm_proxy_delete_device(struct proxy_dev *proxy_dev); > + > +/* > + * Functions related to 'server side' > + */ > + > +/** > + * vtpm_proxy_fops_read - Read TPM commands on 'server side' > + * > + * Return value: > + * Number of bytes read or negative error code > + */ > +static ssize_t vtpm_proxy_fops_read(struct file *filp, char __user *buf, > + size_t count, loff_t *off) > +{ > + struct proxy_dev *proxy_dev = filp->private_data; > + size_t len; > + int sig, rc; > + > + sig = wait_event_interruptible(proxy_dev->wq, proxy_dev->req_len != 0); > + if (sig) > + return -EINTR; > + > + mutex_lock(&proxy_dev->buf_lock); > + > + len = proxy_dev->req_len; > + > + if (count < len) { > + mutex_unlock(&proxy_dev->buf_lock); > + pr_debug("Invalid size in recv: count=%zd, req_len=%zd\n", > + count, len); > + return -EIO; > + } > + > + rc = copy_to_user(buf, proxy_dev->buffer, len); > + memset(proxy_dev->buffer, 0, len); > + proxy_dev->req_len = 0; > + > + if (!rc) > + proxy_dev->state |= STATE_WAIT_RESPONSE_FLAG; > + > + mutex_unlock(&proxy_dev->buf_lock); > + > + if (rc) > + return -EFAULT; > + > + return len; > +} > + > +/** > + * vtpm_proxy_fops_write - Write TPM responses on 'server side' > + * > + * Return value: > + * Number of bytes read or negative error value > + */ > +static ssize_t vtpm_proxy_fops_write(struct file *filp, const char __user *buf, > + size_t count, loff_t *off) > +{ > + struct proxy_dev *proxy_dev = filp->private_data; > + > + mutex_lock(&proxy_dev->buf_lock); > + > + if (count > sizeof(proxy_dev->buffer) || > + !(proxy_dev->state & STATE_WAIT_RESPONSE_FLAG)) { > + mutex_unlock(&proxy_dev->buf_lock); > + return -EIO; > + } > + > + proxy_dev->state &= ~STATE_WAIT_RESPONSE_FLAG; > + > + proxy_dev->req_len = 0; > + > + if (copy_from_user(proxy_dev->buffer, buf, count)) { > + mutex_unlock(&proxy_dev->buf_lock); > + return -EFAULT; > + } > + > + proxy_dev->resp_len = count; > + > + mutex_unlock(&proxy_dev->buf_lock); > + > + wake_up_interruptible(&proxy_dev->wq); > + > + return count; > +} > + > +/* > + * vtpm_proxy_fops_poll: Poll status on 'server side' > + * > + * Return value: > + * Poll flags > + */ > +static unsigned int vtpm_proxy_fops_poll(struct file *filp, poll_table *wait) > +{ > + struct proxy_dev *proxy_dev = filp->private_data; > + unsigned ret; > + > + poll_wait(filp, &proxy_dev->wq, wait); > + > + ret = POLLOUT; > + > + mutex_lock(&proxy_dev->buf_lock); > + > + if (proxy_dev->req_len) > + ret |= POLLIN | POLLRDNORM; > + > + mutex_unlock(&proxy_dev->buf_lock); > + > + return ret; > +} > + > +/* > + * vtpm_proxy_fops_open - Open vTPM device on 'server side' > + * > + * Called when setting up the anonymous file descriptor > + */ > +static void vtpm_proxy_fops_open(struct file *filp) > +{ > + struct proxy_dev *proxy_dev = filp->private_data; > + > + proxy_dev->state |= STATE_OPENED_FLAG; > +} > + > +/** > + * vtpm_proxy_fops_undo_open - counter-part to vtpm_fops_open > + * > + * Call to undo vtpm_proxy_fops_open > + */ > +static void vtpm_proxy_fops_undo_open(struct proxy_dev *proxy_dev) > +{ > + mutex_lock(&proxy_dev->buf_lock); > + > + proxy_dev->state &= ~STATE_OPENED_FLAG; > + > + mutex_unlock(&proxy_dev->buf_lock); > + > + /* no more TPM responses -- wake up anyone waiting for them */ > + wake_up_interruptible(&proxy_dev->wq); > +} > + > +/* > + * vtpm_proxy_fops_release: Close 'server side' > + * > + * Return value: > + * Always returns 0. > + */ > +static int vtpm_proxy_fops_release(struct inode *inode, struct file *filp) > +{ > + struct proxy_dev *proxy_dev = filp->private_data; > + > + filp->private_data = NULL; > + > + vtpm_proxy_delete_device(proxy_dev); > + > + return 0; > +} > + > +static const struct file_operations vtpm_proxy_fops = { > + .owner = THIS_MODULE, > + .llseek = no_llseek, > + .read = vtpm_proxy_fops_read, > + .write = vtpm_proxy_fops_write, > + .poll = vtpm_proxy_fops_poll, > + .release = vtpm_proxy_fops_release, > +}; > + > +/* > + * Functions invoked by the core TPM driver to send TPM commands to > + * 'server side' and receive responses from there. > + */ > + > +/* > + * Called when core TPM driver reads TPM responses from 'server side' > + * > + * Return value: > + * Number of TPM response bytes read, negative error value otherwise > + */ > +static int vtpm_proxy_tpm_op_recv(struct tpm_chip *chip, u8 *buf, size_t count) > +{ > + struct proxy_dev *proxy_dev = chip->vendor.priv; > + size_t len; > + > + if (!proxy_dev) > + return -EIO; > + > + /* process gone ? */ > + mutex_lock(&proxy_dev->buf_lock); > + > + if (!(proxy_dev->state & STATE_OPENED_FLAG)) { > + mutex_unlock(&proxy_dev->buf_lock); > + return -EPIPE; > + } > + > + len = proxy_dev->resp_len; > + if (count < len) { > + dev_err(&chip->dev, > + "Invalid size in recv: count=%zd, resp_len=%zd\n", > + count, len); > + len = -EIO; > + goto out; > + } > + > + memcpy(buf, proxy_dev->buffer, len); > + proxy_dev->resp_len = 0; > + > +out: > + mutex_unlock(&proxy_dev->buf_lock); > + > + return len; > +} > + > +/* > + * Called when core TPM driver forwards TPM requests to 'server side'. > + * > + * Return value: > + * 0 in case of success, negative error value otherwise. > + */ > +static int vtpm_proxy_tpm_op_send(struct tpm_chip *chip, u8 *buf, size_t count) > +{ > + struct proxy_dev *proxy_dev = chip->vendor.priv; > + int rc = 0; > + > + if (!proxy_dev) > + return -EIO; > + > + if (count > sizeof(proxy_dev->buffer)) { > + dev_err(&chip->dev, > + "Invalid size in send: count=%zd, buffer size=%zd\n", > + count, sizeof(proxy_dev->buffer)); > + return -EIO; > + } > + > + mutex_lock(&proxy_dev->buf_lock); > + > + if (!(proxy_dev->state & STATE_OPENED_FLAG)) { > + mutex_unlock(&proxy_dev->buf_lock); > + return -EPIPE; > + } > + > + proxy_dev->resp_len = 0; > + > + proxy_dev->req_len = count; > + memcpy(proxy_dev->buffer, buf, count); > + > + proxy_dev->state &= ~STATE_WAIT_RESPONSE_FLAG; > + > + mutex_unlock(&proxy_dev->buf_lock); > + > + wake_up_interruptible(&proxy_dev->wq); > + > + return rc; > +} > + > +static void vtpm_proxy_tpm_op_cancel(struct tpm_chip *chip) > +{ > + /* not supported */ > +} > + > +static u8 vtpm_proxy_tpm_op_status(struct tpm_chip *chip) > +{ > + struct proxy_dev *proxy_dev = chip->vendor.priv; > + > + if (proxy_dev->resp_len) > + return VTPM_PROXY_REQ_COMPLETE_FLAG; > + > + return 0; > +} > + > +static bool vtpm_proxy_tpm_req_canceled(struct tpm_chip *chip, u8 status) > +{ > + struct proxy_dev *proxy_dev = chip->vendor.priv; > + bool ret; > + > + mutex_lock(&proxy_dev->buf_lock); > + > + ret = !(proxy_dev->state & STATE_OPENED_FLAG); > + > + mutex_unlock(&proxy_dev->buf_lock); > + > + return ret; > +} > + > +static const struct tpm_class_ops vtpm_proxy_tpm_ops = { > + .recv = vtpm_proxy_tpm_op_recv, > + .send = vtpm_proxy_tpm_op_send, > + .cancel = vtpm_proxy_tpm_op_cancel, > + .status = vtpm_proxy_tpm_op_status, > + .req_complete_mask = VTPM_PROXY_REQ_COMPLETE_FLAG, > + .req_complete_val = VTPM_PROXY_REQ_COMPLETE_FLAG, > + .req_canceled = vtpm_proxy_tpm_req_canceled, > +}; > + > +/* > + * Code related to creation and deletion of device pairs > + */ > +static struct proxy_dev *vtpm_proxy_create_proxy_dev(void) > +{ > + struct proxy_dev *proxy_dev; > + struct tpm_chip *chip; > + int err; > + > + proxy_dev = kzalloc(sizeof(*proxy_dev), GFP_KERNEL); > + if (proxy_dev == NULL) > + return ERR_PTR(-ENOMEM); > + > + init_waitqueue_head(&proxy_dev->wq); > + mutex_init(&proxy_dev->buf_lock); > + > + chip = tpm_chip_alloc(NULL, &vtpm_proxy_tpm_ops); > + if (IS_ERR(chip)) { > + err = PTR_ERR(chip); > + goto err_proxy_dev_free; > + } > + chip->vendor.priv = proxy_dev; > + > + proxy_dev->chip = chip; > + > + return proxy_dev; > + > +err_proxy_dev_free: > + kfree(proxy_dev); > + > + return ERR_PTR(err); > +} > + > +/* > + * Undo what has been done in vtpm_create_proxy_dev > + */ > +static inline void vtpm_proxy_delete_proxy_dev(struct proxy_dev *proxy_dev) > +{ > + put_device(&proxy_dev->chip->dev); /* frees chip */ > + kfree(proxy_dev); > +} > + > +/* > + * Create a /dev/tpm%d and 'server side' file descriptor pair > + * > + * Return value: > + * Returns file pointer on success, an error value otherwise > + */ > +static struct file *vtpm_proxy_create_device( > + struct vtpm_proxy_new_dev *vtpm_new_dev) > +{ > + struct proxy_dev *proxy_dev; > + int rc, fd; > + struct file *file; > + > + if (vtpm_new_dev->flags & ~VTPM_PROXY_FLAGS_ALL) > + return ERR_PTR(-EOPNOTSUPP); > + > + proxy_dev = vtpm_proxy_create_proxy_dev(); > + if (IS_ERR(proxy_dev)) > + return ERR_CAST(proxy_dev); > + > + proxy_dev->flags = vtpm_new_dev->flags; > + > + /* setup an anonymous file for the server-side */ > + fd = get_unused_fd_flags(O_RDWR); > + if (fd < 0) { > + rc = fd; > + goto err_delete_proxy_dev; > + } > + > + file = anon_inode_getfile("[vtpms]", &vtpm_proxy_fops, proxy_dev, > + O_RDWR); > + if (IS_ERR(file)) { > + rc = PTR_ERR(file); > + goto err_put_unused_fd; > + } > + > + /* from now on we can unwind with put_unused_fd() + fput() */ > + /* simulate an open() on the server side */ > + vtpm_proxy_fops_open(file); > + > + if (proxy_dev->flags & VTPM_PROXY_FLAG_TPM2) > + proxy_dev->chip->flags |= TPM_CHIP_FLAG_TPM2; > + > + rc = tpm_chip_register(proxy_dev->chip); > + if (rc) > + goto err_vtpm_fput; > + > + vtpm_new_dev->fd = fd; > + vtpm_new_dev->major = MAJOR(proxy_dev->chip->dev.devt); > + vtpm_new_dev->minor = MINOR(proxy_dev->chip->dev.devt); > + vtpm_new_dev->tpm_num = proxy_dev->chip->dev_num; > + > + return file; > + > +err_vtpm_fput: > + put_unused_fd(fd); > + fput(file); > + > + return ERR_PTR(rc); > + > +err_put_unused_fd: > + put_unused_fd(fd); > + > +err_delete_proxy_dev: > + vtpm_proxy_delete_proxy_dev(proxy_dev); > + > + return ERR_PTR(rc); > +} > + > +/* > + * Counter part to vtpm_create_device. > + */ > +static void vtpm_proxy_delete_device(struct proxy_dev *proxy_dev) > +{ > + tpm_chip_unregister(proxy_dev->chip); > + > + vtpm_proxy_fops_undo_open(proxy_dev); > + > + vtpm_proxy_delete_proxy_dev(proxy_dev); > +} > + > +/* > + * Code related to the control device /dev/vtpmx > + */ > + > +/* > + * vtpmx_fops_ioctl: ioctl on /dev/vtpmx > + * > + * Return value: > + * Returns 0 on success, a negative error code otherwise. > + */ > +static long vtpmx_fops_ioctl(struct file *f, unsigned int ioctl, > + unsigned long arg) > +{ > + void __user *argp = (void __user *)arg; > + struct vtpm_proxy_new_dev *vtpm_new_dev_p; > + struct vtpm_proxy_new_dev vtpm_new_dev; > + struct file *file; > + > + switch (ioctl) { > + case VTPM_PROXY_IOC_NEW_DEV: > + if (!capable(CAP_SYS_ADMIN)) > + return -EPERM; > + vtpm_new_dev_p = argp; > + if (copy_from_user(&vtpm_new_dev, vtpm_new_dev_p, > + sizeof(vtpm_new_dev))) > + return -EFAULT; > + file = vtpm_proxy_create_device(&vtpm_new_dev); > + if (IS_ERR(file)) > + return PTR_ERR(file); > + if (copy_to_user(vtpm_new_dev_p, &vtpm_new_dev, > + sizeof(vtpm_new_dev))) { > + put_unused_fd(vtpm_new_dev.fd); > + fput(file); > + return -EFAULT; > + } > + > + fd_install(vtpm_new_dev.fd, file); > + return 0; > + > + default: > + return -ENOIOCTLCMD; > + } > +} > + > +#ifdef CONFIG_COMPAT > +static long vtpmx_fops_compat_ioctl(struct file *f, unsigned int ioctl, > + unsigned long arg) > +{ > + return vtpmx_fops_ioctl(f, ioctl, (unsigned long)compat_ptr(arg)); > +} > +#endif > + > +static const struct file_operations vtpmx_fops = { > + .owner = THIS_MODULE, > + .unlocked_ioctl = vtpmx_fops_ioctl, > +#ifdef CONFIG_COMPAT > + .compat_ioctl = vtpmx_fops_compat_ioctl, > +#endif > + .llseek = noop_llseek, > +}; > + > +static struct miscdevice vtpmx_miscdev = { > + .minor = MISC_DYNAMIC_MINOR, > + .name = "vtpmx", > + .fops = &vtpmx_fops, > +}; > + > +static int vtpmx_init(void) > +{ > + return misc_register(&vtpmx_miscdev); > +} > + > +static void vtpmx_cleanup(void) > +{ > + misc_deregister(&vtpmx_miscdev); > +} > + > +static int __init vtpm_module_init(void) > +{ > + int rc; > + > + rc = vtpmx_init(); > + if (rc) { > + pr_err("couldn't create vtpmx device\n"); > + return rc; > + } > + > + return 0; > +} > + > +static void __exit vtpm_module_exit(void) > +{ > + vtpmx_cleanup(); > +} > + > +module_init(vtpm_module_init); > +module_exit(vtpm_module_exit); > + > +MODULE_AUTHOR("Stefan Berger (stefanb@xxxxxxxxxx)"); > +MODULE_DESCRIPTION("vTPM Driver"); > +MODULE_VERSION("0.1"); > +MODULE_LICENSE("GPL"); > diff --git a/include/uapi/linux/Kbuild b/include/uapi/linux/Kbuild > index ebd10e6..ac767ce 100644 > --- a/include/uapi/linux/Kbuild > +++ b/include/uapi/linux/Kbuild > @@ -449,6 +449,7 @@ header-y += virtio_scsi.h > header-y += virtio_types.h > header-y += vm_sockets.h > header-y += vt.h > +header-y += vtpm_proxy.h > header-y += wait.h > header-y += wanrouter.h > header-y += watchdog.h > diff --git a/include/uapi/linux/vtpm_proxy.h b/include/uapi/linux/vtpm_proxy.h > new file mode 100644 > index 0000000..dc73f00 > --- /dev/null > +++ b/include/uapi/linux/vtpm_proxy.h > @@ -0,0 +1,42 @@ > +/* > + * Definitions for the VTPM proxy driver > + * Copyright (c) 2015, 2016, IBM Corporation > + * > + * This program is free software; you can redistribute it and/or modify it > + * under the terms and conditions of the GNU General Public License, > + * version 2, as published by the Free Software Foundation. > + * > + * This program is distributed in the hope 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. > + */ > + > +#ifndef _UAPI_LINUX_VTPM_PROXY_H > +#define _UAPI_LINUX_VTPM_PROXY_H > + > +#include <linux/types.h> > +#include <linux/ioctl.h> > + > +/* ioctls */ > + > +struct vtpm_proxy_new_dev { > + __u32 flags; /* input */ > + __u32 tpm_num; /* output */ > + __u32 fd; /* output */ > + __u32 major; /* output */ > + __u32 minor; /* output */ > +}; > + > +/* above flags */ > +#define VTPM_PROXY_FLAG_TPM2 1 /* emulator is TPM 2 */ > + > +/* all supported flags */ > +#define VTPM_PROXY_FLAGS_ALL (VTPM_PROXY_FLAG_TPM2) > + > +#define VTPM_PROXY_MAGIC 0xa1 > + > +#define VTPM_PROXY_IOC_NEW_DEV _IOW(VTPM_PROXY_MAGIC, 0x00, \ > + struct vtpm_proxy_new_dev) > + > +#endif /* _UAPI_LINUX_VTPM_PROXY_H */ > -- > 2.4.3 > -- To unsubscribe from this list: send the line "unsubscribe linux-api" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html