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    Subject[PATCH 03/34] sysfs, kernfs: prepare read path for kernfs
    Date
    We're in the process of separating out core sysfs functionality into
    kernfs which will deal with sysfs_dirents directly. This patch
    rearranges read path so that the kernfs and sysfs parts are separate.

    * Regular file read path is refactored such that
    kernfs_seq_start/next/stop/show() handle all the boilerplate work
    including locking and updating event count for poll, while
    sysfs_kf_seq_show() deals with interaction with kobj show method.

    * Bin file read path is refactored such that kernfs_file_direct_read()
    handles all the boilerplate work including buffer management and
    locking, while sysfs_kf_bin_read() deals with interaction with
    bin_attribute read method.

    kernfs_file_read() is added. It invokes either the seq_file or direct
    read path depending on the file type. This will eventually allow
    using the same file_operations for both file types, which is necessary
    to separate out kernfs.

    While this patch changes the order of some operations, it shouldn't
    change any visible behavior.

    v2: Dropped unnecessary zeroing of @count from sysfs_kf_seq_show().
    Add comments explaining single_open() behavior. Both suggested by
    Pavel.

    v3: seq_stop() is called even after seq_start() failed.
    kernfs_seq_start() updated so that it doesn't unlock
    sysfs_open_file->mutex on failure so that kernfs_seq_stop()
    doesn't try to unlock an already unlocked mutex. Reported by
    Fengguang.

    Signed-off-by: Tejun Heo <tj@kernel.org>
    Cc: Pavel Machek <pavel@ucw.cz>
    Cc: Fengguang Wu <fengguang.wu@intel.com>
    ---
    fs/sysfs/file.c | 191 +++++++++++++++++++++++++++++++++++++-------------------
    1 file changed, 126 insertions(+), 65 deletions(-)

    diff --git a/fs/sysfs/file.c b/fs/sysfs/file.c
    index 9b58d87..b695b8b 100644
    --- a/fs/sysfs/file.c
    +++ b/fs/sysfs/file.c
    @@ -86,13 +86,13 @@ static const struct sysfs_ops *sysfs_file_ops(struct sysfs_dirent *sd)
    * details like buffering and seeking. The following function pipes
    * sysfs_ops->show() result through seq_file.
    */
    -static int sysfs_seq_show(struct seq_file *sf, void *v)
    +static int sysfs_kf_seq_show(struct seq_file *sf, void *v)
    {
    struct sysfs_open_file *of = sf->private;
    struct kobject *kobj = of->sd->s_parent->priv;
    - const struct sysfs_ops *ops;
    - char *buf;
    + const struct sysfs_ops *ops = sysfs_file_ops(of->sd);
    ssize_t count;
    + char *buf;

    /* acquire buffer and ensure that it's >= PAGE_SIZE */
    count = seq_get_buf(sf, &buf);
    @@ -102,33 +102,14 @@ static int sysfs_seq_show(struct seq_file *sf, void *v)
    }

    /*
    - * Need @of->sd for attr and ops, its parent for kobj. @of->mutex
    - * nests outside active ref and is just to ensure that the ops
    - * aren't called concurrently for the same open file.
    + * Invoke show(). Control may reach here via seq file lseek even
    + * if @ops->show() isn't implemented.
    */
    - mutex_lock(&of->mutex);
    - if (!sysfs_get_active(of->sd)) {
    - mutex_unlock(&of->mutex);
    - return -ENODEV;
    - }
    -
    - of->event = atomic_read(&of->sd->s_attr.open->event);
    -
    - /*
    - * Lookup @ops and invoke show(). Control may reach here via seq
    - * file lseek even if @ops->show() isn't implemented.
    - */
    - ops = sysfs_file_ops(of->sd);
    - if (ops->show)
    + if (ops->show) {
    count = ops->show(kobj, of->sd->priv, buf);
    - else
    - count = 0;
    -
    - sysfs_put_active(of->sd);
    - mutex_unlock(&of->mutex);
    -
    - if (count < 0)
    - return count;
    + if (count < 0)
    + return count;
    + }

    /*
    * The code works fine with PAGE_SIZE return but it's likely to
    @@ -144,68 +125,146 @@ static int sysfs_seq_show(struct seq_file *sf, void *v)
    return 0;
    }

    -/*
    - * Read method for bin files. As reading a bin file can have side-effects,
    - * the exact offset and bytes specified in read(2) call should be passed to
    - * the read callback making it difficult to use seq_file. Implement
    - * simplistic custom buffering for bin files.
    - */
    -static ssize_t sysfs_bin_read(struct file *file, char __user *userbuf,
    - size_t bytes, loff_t *off)
    +static ssize_t sysfs_kf_bin_read(struct sysfs_open_file *of, char *buf,
    + size_t count, loff_t pos)
    {
    - struct sysfs_open_file *of = sysfs_of(file);
    struct bin_attribute *battr = of->sd->priv;
    struct kobject *kobj = of->sd->s_parent->priv;
    - loff_t size = file_inode(file)->i_size;
    - int count = min_t(size_t, bytes, PAGE_SIZE);
    - loff_t offs = *off;
    - char *buf;
    + loff_t size = file_inode(of->file)->i_size;

    - if (!bytes)
    + if (!count)
    return 0;

    if (size) {
    - if (offs > size)
    + if (pos > size)
    return 0;
    - if (offs + count > size)
    - count = size - offs;
    + if (pos + count > size)
    + count = size - pos;
    }

    - buf = kmalloc(count, GFP_KERNEL);
    + if (!battr->read)
    + return -EIO;
    +
    + return battr->read(of->file, kobj, battr, buf, pos, count);
    +}
    +
    +static void *kernfs_seq_start(struct seq_file *sf, loff_t *ppos)
    +{
    + struct sysfs_open_file *of = sf->private;
    +
    + /*
    + * @of->mutex nests outside active ref and is just to ensure that
    + * the ops aren't called concurrently for the same open file.
    + */
    + mutex_lock(&of->mutex);
    + if (!sysfs_get_active(of->sd))
    + return ERR_PTR(-ENODEV);
    +
    + /*
    + * The same behavior and code as single_open(). Returns !NULL if
    + * pos is at the beginning; otherwise, NULL.
    + */
    + return NULL + !*ppos;
    +}
    +
    +static void *kernfs_seq_next(struct seq_file *sf, void *v, loff_t *ppos)
    +{
    + /*
    + * The same behavior and code as single_open(), always terminate
    + * after the initial read.
    + */
    + ++*ppos;
    + return NULL;
    +}
    +
    +static void kernfs_seq_stop(struct seq_file *sf, void *v)
    +{
    + struct sysfs_open_file *of = sf->private;
    +
    + sysfs_put_active(of->sd);
    + mutex_unlock(&of->mutex);
    +}
    +
    +static int kernfs_seq_show(struct seq_file *sf, void *v)
    +{
    + struct sysfs_open_file *of = sf->private;
    +
    + of->event = atomic_read(&of->sd->s_attr.open->event);
    +
    + return sysfs_kf_seq_show(sf, v);
    +}
    +
    +static const struct seq_operations kernfs_seq_ops = {
    + .start = kernfs_seq_start,
    + .next = kernfs_seq_next,
    + .stop = kernfs_seq_stop,
    + .show = kernfs_seq_show,
    +};
    +
    +/*
    + * As reading a bin file can have side-effects, the exact offset and bytes
    + * specified in read(2) call should be passed to the read callback making
    + * it difficult to use seq_file. Implement simplistic custom buffering for
    + * bin files.
    + */
    +static ssize_t kernfs_file_direct_read(struct sysfs_open_file *of,
    + char __user *user_buf, size_t count,
    + loff_t *ppos)
    +{
    + ssize_t len = min_t(size_t, count, PAGE_SIZE);
    + char *buf;
    +
    + buf = kmalloc(len, GFP_KERNEL);
    if (!buf)
    return -ENOMEM;

    - /* need of->sd for battr, its parent for kobj */
    + /*
    + * @of->mutex nests outside active ref and is just to ensure that
    + * the ops aren't called concurrently for the same open file.
    + */
    mutex_lock(&of->mutex);
    if (!sysfs_get_active(of->sd)) {
    - count = -ENODEV;
    + len = -ENODEV;
    mutex_unlock(&of->mutex);
    goto out_free;
    }

    - if (battr->read)
    - count = battr->read(file, kobj, battr, buf, offs, count);
    - else
    - count = -EIO;
    + len = sysfs_kf_bin_read(of, buf, len, *ppos);

    sysfs_put_active(of->sd);
    mutex_unlock(&of->mutex);

    - if (count < 0)
    + if (len < 0)
    goto out_free;

    - if (copy_to_user(userbuf, buf, count)) {
    - count = -EFAULT;
    + if (copy_to_user(user_buf, buf, len)) {
    + len = -EFAULT;
    goto out_free;
    }

    - pr_debug("offs = %lld, *off = %lld, count = %d\n", offs, *off, count);
    -
    - *off = offs + count;
    + *ppos += len;

    out_free:
    kfree(buf);
    - return count;
    + return len;
    +}
    +
    +/**
    + * kernfs_file_read - kernfs vfs read callback
    + * @file: file pointer
    + * @user_buf: data to write
    + * @count: number of bytes
    + * @ppos: starting offset
    + */
    +static ssize_t kernfs_file_read(struct file *file, char __user *user_buf,
    + size_t count, loff_t *ppos)
    +{
    + struct sysfs_open_file *of = sysfs_of(file);
    +
    + if (sysfs_is_bin(of->sd))
    + return kernfs_file_direct_read(of, user_buf, count, ppos);
    + else
    + return seq_read(file, user_buf, count, ppos);
    }

    /**
    @@ -677,12 +736,14 @@ static int sysfs_open_file(struct inode *inode, struct file *file)
    * and readable regular files are the vast majority anyway.
    */
    if (sysfs_is_bin(attr_sd))
    - error = single_open(file, NULL, of);
    + error = seq_open(file, NULL);
    else
    - error = single_open(file, sysfs_seq_show, of);
    + error = seq_open(file, &kernfs_seq_ops);
    if (error)
    goto err_free;

    + ((struct seq_file *)file->private_data)->private = of;
    +
    /* seq_file clears PWRITE unconditionally, restore it if WRITE */
    if (file->f_mode & FMODE_WRITE)
    file->f_mode |= FMODE_PWRITE;
    @@ -697,7 +758,7 @@ static int sysfs_open_file(struct inode *inode, struct file *file)
    return 0;

    err_close:
    - single_release(inode, file);
    + seq_release(inode, file);
    err_free:
    kfree(of);
    err_out:
    @@ -711,7 +772,7 @@ static int sysfs_release(struct inode *inode, struct file *filp)
    struct sysfs_open_file *of = sysfs_of(filp);

    sysfs_put_open_dirent(sd, of);
    - single_release(inode, filp);
    + seq_release(inode, filp);
    kfree(of);

    return 0;
    @@ -816,7 +877,7 @@ void sysfs_notify(struct kobject *k, const char *dir, const char *attr)
    EXPORT_SYMBOL_GPL(sysfs_notify);

    const struct file_operations sysfs_file_operations = {
    - .read = seq_read,
    + .read = kernfs_file_read,
    .write = sysfs_write_file,
    .llseek = generic_file_llseek,
    .open = sysfs_open_file,
    @@ -825,7 +886,7 @@ const struct file_operations sysfs_file_operations = {
    };

    const struct file_operations sysfs_bin_operations = {
    - .read = sysfs_bin_read,
    + .read = kernfs_file_read,
    .write = sysfs_write_file,
    .llseek = generic_file_llseek,
    .mmap = sysfs_bin_mmap,
    --
    1.8.4.2


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