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SubjectRe: [GIT] /proc/uptime fix


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. Maybe it's
something as trivial as just flushing the buffer whenever 'pos' doesn't
match f_pos?

ie something like the following (TOTALLY UNTESTED!)

I may be way off base here, Al needs to whack some sense into this.

Linus

---
fs/seq_file.c | 8 ++++++--
1 files changed, 6 insertions(+), 2 deletions(-)

diff --git a/fs/seq_file.c b/fs/seq_file.c
index eba2eab..eb95ec9 100644
--- 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);
return 0;
}
EXPORT_SYMBOL(seq_open);
@@ -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;
mutex_unlock(&m->lock);
return copied;
Enomem:

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