Messages in this thread | | | Date | Mon, 3 Nov 2008 23:25:44 +0300 | From | Alexey Dobriyan <> | Subject | Re: [GIT] /proc/uptime fix |
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On Mon, Nov 03, 2008 at 10:14:16AM -0800, Linus Torvalds wrote: > On Mon, 3 Nov 2008, Alexey Dobriyan wrote: > > > > Alexey Dobriyan (1): > > proc: revert /proc/uptime to ->read_proc hook > > Ok, pulled, but it's a bit sad. > > Al: the commit is 6c87df37dcb9c6c33923707fa5191e0a65874d60, and the > message explains it all: > > Turned out some VMware userspace does pread(2) on /proc/uptime, but > seqfiles currently don't allow pread() resulting in -ESPIPE. > > Seqfiles in theory can do pread(), but this can be a long story, > so revert to ->read_proc until then. > > and I bet that the pread() usage is just with a constant loff_t of 0, and > just there to avoid a simple case of "lseek+read". > > I wonder how hard it is to make seqfiles support pread.
Not hard at all, if ->read hook has information if it's called from read(2) or pread(2) (or something equivalent).
> Maybe it's something as trivial as just flushing the buffer whenever 'pos' > doesn't match f_pos?
> --- a/fs/seq_file.c > +++ b/fs/seq_file.c > @@ -48,8 +48,8 @@ int seq_open(struct file *file, const struct seq_operations *op) > */ > file->f_version = 0; > > - /* SEQ files support lseek, but not pread/pwrite */ > - file->f_mode &= ~(FMODE_PREAD | FMODE_PWRITE); > + /* SEQ files support lseek, but not pwrite */ > + file->f_mode &= ~(FMODE_PWRITE);
FMODE_PWRITE is aliased to FMODE_PREAD so you have to split them first. ;-)
> @@ -91,6 +91,8 @@ ssize_t seq_read(struct file *file, char __user *buf, size_t size, loff_t *ppos) > if (!m->buf) > goto Enomem; > } > + if (pos != file->f_pos) > + m->count = 0; > /* if not empty - flush it first */ > if (m->count) { > n = min(m->count, size); > @@ -175,6 +177,8 @@ Done: > else > *ppos += copied; > file->f_version = m->version; > + if (pos != file->f_pos) > + m->count = 0;
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