From fcbf94b9dedd2ce08e798a99aafc94fec8668161 Mon Sep 17 00:00:00 2001 From: Linus Torvalds Date: Sat, 28 Apr 2012 08:29:56 -0700 Subject: Revert "autofs: work around unhappy compat problem on x86-64" This reverts commit a32744d4abae24572eff7269bc17895c41bd0085. While that commit was technically the right thing to do, and made the x86-64 compat mode work identically to native 32-bit mode (and thus fixing the problem with a 32-bit systemd install on a 64-bit kernel), it turns out that the automount binaries had workarounds for this compat problem. Now, the workarounds are disgusting: doing an "uname()" to find out the architecture of the kernel, and then comparing it for the 64-bit cases and fixing up the size of the read() in automount for those. And they were confused: it's not actually a generic 64-bit issue at all, it's very much tied to just x86-64, which has different alignment for an 'u64' in 64-bit mode than in 32-bit mode. But the end result is that fixing the compat layer actually breaks the case of a 32-bit automount on a x86-64 kernel. There are various approaches to fix this (including just doing a "strcmp()" on current->comm and comparing it to "automount"), but I think that I will do the one that teaches pipes about a special "packet mode", which will allow user space to not have to care too deeply about the padding at the end of the autofs packet. That change will make the compat workaround unnecessary, so let's revert it first, and get automount working again in compat mode. The packetized pipes will then fix autofs for systemd. Reported-and-requested-by: Michael Tokarev Cc: Ian Kent Cc: stable@kernel.org # for 3.3 Signed-off-by: Linus Torvalds --- fs/autofs4/inode.c | 2 -- 1 file changed, 2 deletions(-) (limited to 'fs/autofs4/inode.c') diff --git a/fs/autofs4/inode.c b/fs/autofs4/inode.c index d8dc002e9cc3..14c7bc02349e 100644 --- a/fs/autofs4/inode.c +++ b/fs/autofs4/inode.c @@ -19,7 +19,6 @@ #include #include #include -#include #include "autofs_i.h" #include @@ -225,7 +224,6 @@ int autofs4_fill_super(struct super_block *s, void *data, int silent) set_autofs_type_indirect(&sbi->type); sbi->min_proto = 0; sbi->max_proto = 0; - sbi->compat_daemon = is_compat_task(); mutex_init(&sbi->wq_mutex); mutex_init(&sbi->pipe_mutex); spin_lock_init(&sbi->fs_lock); -- cgit v1.2.3-58-ga151 From 64f371bc3107e69efce563a3d0f0e6880de0d537 Mon Sep 17 00:00:00 2001 From: Linus Torvalds Date: Sun, 29 Apr 2012 13:30:08 -0700 Subject: autofs: make the autofsv5 packet file descriptor use a packetized pipe The autofs packet size has had a very unfortunate size problem on x86: because the alignment of 'u64' differs in 32-bit and 64-bit modes, and because the packet data was not 8-byte aligned, the size of the autofsv5 packet structure differed between 32-bit and 64-bit modes despite looking otherwise identical (300 vs 304 bytes respectively). We first fixed that up by making the 64-bit compat mode know about this problem in commit a32744d4abae ("autofs: work around unhappy compat problem on x86-64"), and that made a 32-bit 'systemd' work happily on a 64-bit kernel because everything then worked the same way as on a 32-bit kernel. But it turned out that 'automount' had actually known and worked around this problem in user space, so fixing the kernel to do the proper 32-bit compatibility handling actually *broke* 32-bit automount on a 64-bit kernel, because it knew that the packet sizes were wrong and expected those incorrect sizes. As a result, we ended up reverting that compatibility mode fix, and thus breaking systemd again, in commit fcbf94b9dedd. With both automount and systemd doing a single read() system call, and verifying that they get *exactly* the size they expect but using different sizes, it seemed that fixing one of them inevitably seemed to break the other. At one point, a patch I seriously considered applying from Michael Tokarev did a "strcmp()" to see if it was automount that was doing the operation. Ugly, ugly. However, a prettier solution exists now thanks to the packetized pipe mode. By marking the communication pipe as being packetized (by simply setting the O_DIRECT flag), we can always just write the bigger packet size, and if user-space does a smaller read, it will just get that partial end result and the extra alignment padding will simply be thrown away. This makes both automount and systemd happy, since they now get the size they asked for, and the kernel side of autofs simply no longer needs to care - it could pad out the packet arbitrarily. Of course, if there is some *other* user of autofs (please, please, please tell me it ain't so - and we haven't heard of any) that tries to read the packets with multiple writes, that other user will now be broken - the whole point of the packetized mode is that one system call gets exactly one packet, and you cannot read a packet in pieces. Tested-by: Michael Tokarev Cc: Alan Cox Cc: David Miller Cc: Ian Kent Cc: Thomas Meyer Cc: stable@kernel.org Signed-off-by: Linus Torvalds --- fs/autofs4/autofs_i.h | 11 +++++++++++ fs/autofs4/dev-ioctl.c | 2 +- fs/autofs4/inode.c | 2 +- 3 files changed, 13 insertions(+), 2 deletions(-) (limited to 'fs/autofs4/inode.c') diff --git a/fs/autofs4/autofs_i.h b/fs/autofs4/autofs_i.h index d8d8e7ba6a1e..908e18455413 100644 --- a/fs/autofs4/autofs_i.h +++ b/fs/autofs4/autofs_i.h @@ -269,6 +269,17 @@ int autofs4_fill_super(struct super_block *, void *, int); struct autofs_info *autofs4_new_ino(struct autofs_sb_info *); void autofs4_clean_ino(struct autofs_info *); +static inline int autofs_prepare_pipe(struct file *pipe) +{ + if (!pipe->f_op || !pipe->f_op->write) + return -EINVAL; + if (!S_ISFIFO(pipe->f_dentry->d_inode->i_mode)) + return -EINVAL; + /* We want a packet pipe */ + pipe->f_flags |= O_DIRECT; + return 0; +} + /* Queue management functions */ int autofs4_wait(struct autofs_sb_info *,struct dentry *, enum autofs_notify); diff --git a/fs/autofs4/dev-ioctl.c b/fs/autofs4/dev-ioctl.c index 3dfd615afb6b..aa9103f8f01b 100644 --- a/fs/autofs4/dev-ioctl.c +++ b/fs/autofs4/dev-ioctl.c @@ -376,7 +376,7 @@ static int autofs_dev_ioctl_setpipefd(struct file *fp, err = -EBADF; goto out; } - if (!pipe->f_op || !pipe->f_op->write) { + if (autofs_prepare_pipe(pipe) < 0) { err = -EPIPE; fput(pipe); goto out; diff --git a/fs/autofs4/inode.c b/fs/autofs4/inode.c index 14c7bc02349e..6e488ebe7784 100644 --- a/fs/autofs4/inode.c +++ b/fs/autofs4/inode.c @@ -290,7 +290,7 @@ int autofs4_fill_super(struct super_block *s, void *data, int silent) printk("autofs: could not open pipe file descriptor\n"); goto fail_dput; } - if (!pipe->f_op || !pipe->f_op->write) + if (autofs_prepare_pipe(pipe) < 0) goto fail_fput; sbi->pipe = pipe; sbi->pipefd = pipefd; -- cgit v1.2.3-58-ga151