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    SubjectRe: [patch] pipe: add support for shrinking and growing pipes
    On 2010-06-03 13:32, Miklos Szeredi wrote:
    > On Thu, 03 Jun 2010, Jens Axboe wrote:
    >> I looked at that when I did the original pipe-max-pages, but it seems
    >> we're not consistent in this regard. Anyway, here's what I came up with.
    >> Not tested yet, and I hope thunderbird doesn't fsck up the patch.
    >
    > Unfortunately it did (line wrap damage).

    I suspected it might. This better?

    diff --git a/fs/pipe.c b/fs/pipe.c
    index f98fae3..f7f62f3 100644
    --- a/fs/pipe.c
    +++ b/fs/pipe.c
    @@ -26,9 +26,14 @@

    /*
    * The max size that a non-root user is allowed to grow the pipe. Can
    - * be set by root in /proc/sys/fs/pipe-max-pages
    + * be set by root in /proc/sys/fs/pipe_max_size
    */
    -unsigned int pipe_max_pages = PIPE_DEF_BUFFERS * 16;
    +unsigned int pipe_max_size = 1048576;
    +
    +/*
    + * Minimum pipe size, as required by POSIX
    + */
    +unsigned int pipe_min_size = PAGE_SIZE;

    /*
    * We use a start+len construction, which provides full use of the
    @@ -1156,6 +1161,35 @@ static long pipe_set_size(struct pipe_inode_info *pipe, unsigned long nr_pages)
    return nr_pages * PAGE_SIZE;
    }

    +/*
    + * Currently we rely on the pipe array holding a power-of-2 number
    + * of pages.
    + */
    +static inline unsigned int round_pipe_size(unsigned int size)
    +{
    + unsigned long nr_pages;
    +
    + nr_pages = (size + PAGE_SIZE - 1) >> PAGE_SHIFT;
    + return roundup_pow_of_two(nr_pages) << PAGE_SHIFT;
    +}
    +
    +/*
    + * This should work even if CONFIG_PROC_FS isn't set, as proc_dointvec_minmax
    + * will return an error.
    + */
    +int pipe_proc_fn(struct ctl_table *table, int write, void __user *buf,
    + size_t *lenp, loff_t *ppos)
    +{
    + int ret;
    +
    + ret = proc_dointvec_minmax(table, write, buf, lenp, ppos);
    + if (ret < 0 || !write)
    + return ret;
    +
    + pipe_max_size = round_pipe_size(pipe_max_size);
    + return ret;
    +}
    +
    long pipe_fcntl(struct file *file, unsigned int cmd, unsigned long arg)
    {
    struct pipe_inode_info *pipe;
    @@ -1169,23 +1203,19 @@ long pipe_fcntl(struct file *file, unsigned int cmd, unsigned long arg)

    switch (cmd) {
    case F_SETPIPE_SZ: {
    - unsigned long nr_pages;
    + unsigned int size, nr_pages;

    - /*
    - * Currently the array must be a power-of-2 size, so adjust
    - * upwards if needed.
    - */
    - nr_pages = (arg + PAGE_SIZE - 1) >> PAGE_SHIFT;
    - nr_pages = roundup_pow_of_two(nr_pages);
    + size = round_pipe_size(arg);
    + nr_pages = size >> PAGE_SHIFT;

    - if (!capable(CAP_SYS_RESOURCE) && nr_pages > pipe_max_pages) {
    + if (!capable(CAP_SYS_RESOURCE) && size > pipe_max_size) {
    ret = -EPERM;
    goto out;
    - } else if (nr_pages < 1) {
    + } else if (nr_pages < PAGE_SIZE) {
    ret = -EINVAL;
    goto out;
    }
    - ret = pipe_set_size(pipe, arg);
    + ret = pipe_set_size(pipe, nr_pages);
    break;
    }
    case F_GETPIPE_SZ:
    diff --git a/include/linux/pipe_fs_i.h b/include/linux/pipe_fs_i.h
    index 16de393..4457969 100644
    --- a/include/linux/pipe_fs_i.h
    +++ b/include/linux/pipe_fs_i.h
    @@ -139,7 +139,9 @@ void pipe_lock(struct pipe_inode_info *);
    void pipe_unlock(struct pipe_inode_info *);
    void pipe_double_lock(struct pipe_inode_info *, struct pipe_inode_info *);

    -extern unsigned int pipe_max_pages;
    +extern unsigned int pipe_max_size, pipe_min_size;
    +int pipe_proc_fn(struct ctl_table *, int, void __user *, size_t *, loff_t *);
    +

    /* Drop the inode semaphore and wait for a pipe event, atomically */
    void pipe_wait(struct pipe_inode_info *pipe);
    diff --git a/kernel/sysctl.c b/kernel/sysctl.c
    index 997080f..2f9b3a6 100644
    --- a/kernel/sysctl.c
    +++ b/kernel/sysctl.c
    @@ -1471,12 +1471,12 @@ static struct ctl_table fs_table[] = {
    },
    #endif
    {
    - .procname = "pipe-max-pages",
    - .data = &pipe_max_pages,
    + .procname = "pipe_max_size",
    + .data = &pipe_max_size,
    .maxlen = sizeof(int),
    .mode = 0644,
    - .proc_handler = &proc_dointvec_minmax,
    - .extra1 = &two,
    + .proc_handler = &pipe_proc_fn,
    + .extra1 = &pipe_min_size,
    },
    /*
    * NOTE: do not add new entries to this table unless you have read
    --
    Jens Axboe



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