diff options
Diffstat (limited to 'target/linux/brcm2708/patches-4.4/0177-configfs-implement-binary-attributes.patch')
| -rw-r--r-- | target/linux/brcm2708/patches-4.4/0177-configfs-implement-binary-attributes.patch | 639 |
1 files changed, 639 insertions, 0 deletions
diff --git a/target/linux/brcm2708/patches-4.4/0177-configfs-implement-binary-attributes.patch b/target/linux/brcm2708/patches-4.4/0177-configfs-implement-binary-attributes.patch new file mode 100644 index 0000000000..bb500ed5a4 --- /dev/null +++ b/target/linux/brcm2708/patches-4.4/0177-configfs-implement-binary-attributes.patch @@ -0,0 +1,639 @@ +From 28059745722d31f48971035bbca98d689adb41f6 Mon Sep 17 00:00:00 2001 +From: Pantelis Antoniou <pantelis.antoniou@konsulko.com> +Date: Thu, 22 Oct 2015 23:30:04 +0300 +Subject: [PATCH 177/304] configfs: implement binary attributes + +ConfigFS lacked binary attributes up until now. This patch +introduces support for binary attributes in a somewhat similar +manner of sysfs binary attributes albeit with changes that +fit the configfs usage model. + +Problems that configfs binary attributes fix are everything that +requires a binary blob as part of the configuration of a resource, +such as bitstream loading for FPGAs, DTBs for dynamically created +devices etc. + +Look at Documentation/filesystems/configfs/configfs.txt for internals +and howto use them. + +This patch is against linux-next as of today that contains +Christoph's configfs rework. + +Signed-off-by: Pantelis Antoniou <pantelis.antoniou@konsulko.com> +[hch: folded a fix from Geert Uytterhoeven <geert+renesas@glider.be>] +[hch: a few tiny updates based on review feedback] +Signed-off-by: Christoph Hellwig <hch@lst.de> +--- + Documentation/filesystems/configfs/configfs.txt | 57 +++++- + fs/configfs/configfs_internal.h | 14 +- + fs/configfs/dir.c | 18 +- + fs/configfs/file.c | 255 +++++++++++++++++++++++- + fs/configfs/inode.c | 2 +- + include/linux/configfs.h | 50 +++++ + 6 files changed, 374 insertions(+), 22 deletions(-) + +--- a/Documentation/filesystems/configfs/configfs.txt ++++ b/Documentation/filesystems/configfs/configfs.txt +@@ -51,15 +51,27 @@ configfs tree is always there, whether m + An item is created via mkdir(2). The item's attributes will also + appear at this time. readdir(3) can determine what the attributes are, + read(2) can query their default values, and write(2) can store new +-values. Like sysfs, attributes should be ASCII text files, preferably +-with only one value per file. The same efficiency caveats from sysfs +-apply. Don't mix more than one attribute in one attribute file. +- +-Like sysfs, configfs expects write(2) to store the entire buffer at +-once. When writing to configfs attributes, userspace processes should +-first read the entire file, modify the portions they wish to change, and +-then write the entire buffer back. Attribute files have a maximum size +-of one page (PAGE_SIZE, 4096 on i386). ++values. Don't mix more than one attribute in one attribute file. ++ ++There are two types of configfs attributes: ++ ++* Normal attributes, which similar to sysfs attributes, are small ASCII text ++files, with a maximum size of one page (PAGE_SIZE, 4096 on i386). Preferably ++only one value per file should be used, and the same caveats from sysfs apply. ++Configfs expects write(2) to store the entire buffer at once. When writing to ++normal configfs attributes, userspace processes should first read the entire ++file, modify the portions they wish to change, and then write the entire ++buffer back. ++ ++* Binary attributes, which are somewhat similar to sysfs binary attributes, ++but with a few slight changes to semantics. The PAGE_SIZE limitation does not ++apply, but the whole binary item must fit in single kernel vmalloc'ed buffer. ++The write(2) calls from user space are buffered, and the attributes' ++write_bin_attribute method will be invoked on the final close, therefore it is ++imperative for user-space to check the return code of close(2) in order to ++verify that the operation finished successfully. ++To avoid a malicious user OOMing the kernel, there's a per-binary attribute ++maximum buffer value. + + When an item needs to be destroyed, remove it with rmdir(2). An + item cannot be destroyed if any other item has a link to it (via +@@ -171,6 +183,7 @@ among other things. For that, it needs + struct configfs_item_operations *ct_item_ops; + struct configfs_group_operations *ct_group_ops; + struct configfs_attribute **ct_attrs; ++ struct configfs_bin_attribute **ct_bin_attrs; + }; + + The most basic function of a config_item_type is to define what +@@ -201,6 +214,32 @@ be called whenever userspace asks for a + attribute is writable and provides a ->store method, that method will be + be called whenever userspace asks for a write(2) on the attribute. + ++[struct configfs_bin_attribute] ++ ++ struct configfs_attribute { ++ struct configfs_attribute cb_attr; ++ void *cb_private; ++ size_t cb_max_size; ++ }; ++ ++The binary attribute is used when the one needs to use binary blob to ++appear as the contents of a file in the item's configfs directory. ++To do so add the binary attribute to the NULL-terminated array ++config_item_type->ct_bin_attrs, and the item appears in configfs, the ++attribute file will appear with the configfs_bin_attribute->cb_attr.ca_name ++filename. configfs_bin_attribute->cb_attr.ca_mode specifies the file ++permissions. ++The cb_private member is provided for use by the driver, while the ++cb_max_size member specifies the maximum amount of vmalloc buffer ++to be used. ++ ++If binary attribute is readable and the config_item provides a ++ct_item_ops->read_bin_attribute() method, that method will be called ++whenever userspace asks for a read(2) on the attribute. The converse ++will happen for write(2). The reads/writes are bufferred so only a ++single read/write will occur; the attributes' need not concern itself ++with it. ++ + [struct config_group] + + A config_item cannot live in a vacuum. The only way one can be created +--- a/fs/configfs/configfs_internal.h ++++ b/fs/configfs/configfs_internal.h +@@ -53,13 +53,14 @@ struct configfs_dirent { + #define CONFIGFS_ROOT 0x0001 + #define CONFIGFS_DIR 0x0002 + #define CONFIGFS_ITEM_ATTR 0x0004 ++#define CONFIGFS_ITEM_BIN_ATTR 0x0008 + #define CONFIGFS_ITEM_LINK 0x0020 + #define CONFIGFS_USET_DIR 0x0040 + #define CONFIGFS_USET_DEFAULT 0x0080 + #define CONFIGFS_USET_DROPPING 0x0100 + #define CONFIGFS_USET_IN_MKDIR 0x0200 + #define CONFIGFS_USET_CREATING 0x0400 +-#define CONFIGFS_NOT_PINNED (CONFIGFS_ITEM_ATTR) ++#define CONFIGFS_NOT_PINNED (CONFIGFS_ITEM_ATTR | CONFIGFS_ITEM_BIN_ATTR) + + extern struct mutex configfs_symlink_mutex; + extern spinlock_t configfs_dirent_lock; +@@ -72,6 +73,8 @@ extern struct inode * configfs_new_inode + extern int configfs_create(struct dentry *, umode_t mode, void (*init)(struct inode *)); + + extern int configfs_create_file(struct config_item *, const struct configfs_attribute *); ++extern int configfs_create_bin_file(struct config_item *, ++ const struct configfs_bin_attribute *); + extern int configfs_make_dirent(struct configfs_dirent *, + struct dentry *, void *, umode_t, int); + extern int configfs_dirent_is_ready(struct configfs_dirent *); +@@ -88,7 +91,7 @@ extern void configfs_release_fs(void); + extern struct rw_semaphore configfs_rename_sem; + extern const struct file_operations configfs_dir_operations; + extern const struct file_operations configfs_file_operations; +-extern const struct file_operations bin_fops; ++extern const struct file_operations configfs_bin_file_operations; + extern const struct inode_operations configfs_dir_inode_operations; + extern const struct inode_operations configfs_root_inode_operations; + extern const struct inode_operations configfs_symlink_inode_operations; +@@ -119,6 +122,13 @@ static inline struct configfs_attribute + return ((struct configfs_attribute *) sd->s_element); + } + ++static inline struct configfs_bin_attribute *to_bin_attr(struct dentry *dentry) ++{ ++ struct configfs_attribute *attr = to_attr(dentry); ++ ++ return container_of(attr, struct configfs_bin_attribute, cb_attr); ++} ++ + static inline struct config_item *configfs_get_config_item(struct dentry *dentry) + { + struct config_item * item = NULL; +--- a/fs/configfs/dir.c ++++ b/fs/configfs/dir.c +@@ -255,6 +255,12 @@ static void configfs_init_file(struct in + inode->i_fop = &configfs_file_operations; + } + ++static void configfs_init_bin_file(struct inode *inode) ++{ ++ inode->i_size = 0; ++ inode->i_fop = &configfs_bin_file_operations; ++} ++ + static void init_symlink(struct inode * inode) + { + inode->i_op = &configfs_symlink_inode_operations; +@@ -423,7 +429,9 @@ static int configfs_attach_attr(struct c + spin_unlock(&configfs_dirent_lock); + + error = configfs_create(dentry, (attr->ca_mode & S_IALLUGO) | S_IFREG, +- configfs_init_file); ++ (sd->s_type & CONFIGFS_ITEM_BIN_ATTR) ? ++ configfs_init_bin_file : ++ configfs_init_file); + if (error) { + configfs_put(sd); + return error; +@@ -583,6 +591,7 @@ static int populate_attrs(struct config_ + { + struct config_item_type *t = item->ci_type; + struct configfs_attribute *attr; ++ struct configfs_bin_attribute *bin_attr; + int error = 0; + int i; + +@@ -594,6 +603,13 @@ static int populate_attrs(struct config_ + break; + } + } ++ if (t->ct_bin_attrs) { ++ for (i = 0; (bin_attr = t->ct_bin_attrs[i]) != NULL; i++) { ++ error = configfs_create_bin_file(item, bin_attr); ++ if (error) ++ break; ++ } ++ } + + if (error) + detach_attrs(item); +--- a/fs/configfs/file.c ++++ b/fs/configfs/file.c +@@ -28,6 +28,7 @@ + #include <linux/module.h> + #include <linux/slab.h> + #include <linux/mutex.h> ++#include <linux/vmalloc.h> + #include <asm/uaccess.h> + + #include <linux/configfs.h> +@@ -48,6 +49,10 @@ struct configfs_buffer { + struct configfs_item_operations * ops; + struct mutex mutex; + int needs_read_fill; ++ bool read_in_progress; ++ bool write_in_progress; ++ char *bin_buffer; ++ int bin_buffer_size; + }; + + +@@ -123,6 +128,87 @@ out: + return retval; + } + ++/** ++ * configfs_read_bin_file - read a binary attribute. ++ * @file: file pointer. ++ * @buf: buffer to fill. ++ * @count: number of bytes to read. ++ * @ppos: starting offset in file. ++ * ++ * Userspace wants to read a binary attribute file. The attribute ++ * descriptor is in the file's ->d_fsdata. The target item is in the ++ * directory's ->d_fsdata. ++ * ++ * We check whether we need to refill the buffer. If so we will ++ * call the attributes' attr->read() twice. The first time we ++ * will pass a NULL as a buffer pointer, which the attributes' method ++ * will use to return the size of the buffer required. If no error ++ * occurs we will allocate the buffer using vmalloc and call ++ * attr->read() again passing that buffer as an argument. ++ * Then we just copy to user-space using simple_read_from_buffer. ++ */ ++ ++static ssize_t ++configfs_read_bin_file(struct file *file, char __user *buf, ++ size_t count, loff_t *ppos) ++{ ++ struct configfs_buffer *buffer = file->private_data; ++ struct dentry *dentry = file->f_path.dentry; ++ struct config_item *item = to_item(dentry->d_parent); ++ struct configfs_bin_attribute *bin_attr = to_bin_attr(dentry); ++ ssize_t retval = 0; ++ ssize_t len = min_t(size_t, count, PAGE_SIZE); ++ ++ mutex_lock(&buffer->mutex); ++ ++ /* we don't support switching read/write modes */ ++ if (buffer->write_in_progress) { ++ retval = -ETXTBSY; ++ goto out; ++ } ++ buffer->read_in_progress = 1; ++ ++ if (buffer->needs_read_fill) { ++ /* perform first read with buf == NULL to get extent */ ++ len = bin_attr->read(item, NULL, 0); ++ if (len <= 0) { ++ retval = len; ++ goto out; ++ } ++ ++ /* do not exceed the maximum value */ ++ if (bin_attr->cb_max_size && len > bin_attr->cb_max_size) { ++ retval = -EFBIG; ++ goto out; ++ } ++ ++ buffer->bin_buffer = vmalloc(len); ++ if (buffer->bin_buffer == NULL) { ++ retval = -ENOMEM; ++ goto out; ++ } ++ buffer->bin_buffer_size = len; ++ ++ /* perform second read to fill buffer */ ++ len = bin_attr->read(item, buffer->bin_buffer, len); ++ if (len < 0) { ++ retval = len; ++ vfree(buffer->bin_buffer); ++ buffer->bin_buffer_size = 0; ++ buffer->bin_buffer = NULL; ++ goto out; ++ } ++ ++ buffer->needs_read_fill = 0; ++ } ++ ++ retval = simple_read_from_buffer(buf, count, ppos, buffer->bin_buffer, ++ buffer->bin_buffer_size); ++out: ++ mutex_unlock(&buffer->mutex); ++ return retval; ++} ++ + + /** + * fill_write_buffer - copy buffer from userspace. +@@ -209,10 +295,80 @@ configfs_write_file(struct file *file, c + return len; + } + +-static int check_perm(struct inode * inode, struct file * file) ++/** ++ * configfs_write_bin_file - write a binary attribute. ++ * @file: file pointer ++ * @buf: data to write ++ * @count: number of bytes ++ * @ppos: starting offset ++ * ++ * Writing to a binary attribute file is similar to a normal read. ++ * We buffer the consecutive writes (binary attribute files do not ++ * support lseek) in a continuously growing buffer, but we don't ++ * commit until the close of the file. ++ */ ++ ++static ssize_t ++configfs_write_bin_file(struct file *file, const char __user *buf, ++ size_t count, loff_t *ppos) ++{ ++ struct configfs_buffer *buffer = file->private_data; ++ struct dentry *dentry = file->f_path.dentry; ++ struct configfs_bin_attribute *bin_attr = to_bin_attr(dentry); ++ void *tbuf = NULL; ++ ssize_t len; ++ ++ mutex_lock(&buffer->mutex); ++ ++ /* we don't support switching read/write modes */ ++ if (buffer->read_in_progress) { ++ len = -ETXTBSY; ++ goto out; ++ } ++ buffer->write_in_progress = 1; ++ ++ /* buffer grows? */ ++ if (*ppos + count > buffer->bin_buffer_size) { ++ ++ if (bin_attr->cb_max_size && ++ *ppos + count > bin_attr->cb_max_size) { ++ len = -EFBIG; ++ } ++ ++ tbuf = vmalloc(*ppos + count); ++ if (tbuf == NULL) { ++ len = -ENOMEM; ++ goto out; ++ } ++ ++ /* copy old contents */ ++ if (buffer->bin_buffer) { ++ memcpy(tbuf, buffer->bin_buffer, ++ buffer->bin_buffer_size); ++ vfree(buffer->bin_buffer); ++ } ++ ++ /* clear the new area */ ++ memset(tbuf + buffer->bin_buffer_size, 0, ++ *ppos + count - buffer->bin_buffer_size); ++ buffer->bin_buffer = tbuf; ++ buffer->bin_buffer_size = *ppos + count; ++ } ++ ++ len = simple_write_to_buffer(buffer->bin_buffer, ++ buffer->bin_buffer_size, ppos, buf, count); ++ if (len > 0) ++ *ppos += len; ++out: ++ mutex_unlock(&buffer->mutex); ++ return len; ++} ++ ++static int check_perm(struct inode * inode, struct file * file, int type) + { + struct config_item *item = configfs_get_config_item(file->f_path.dentry->d_parent); + struct configfs_attribute * attr = to_attr(file->f_path.dentry); ++ struct configfs_bin_attribute *bin_attr = NULL; + struct configfs_buffer * buffer; + struct configfs_item_operations * ops = NULL; + int error = 0; +@@ -220,6 +376,9 @@ static int check_perm(struct inode * ino + if (!item || !attr) + goto Einval; + ++ if (type & CONFIGFS_ITEM_BIN_ATTR) ++ bin_attr = to_bin_attr(file->f_path.dentry); ++ + /* Grab the module reference for this attribute if we have one */ + if (!try_module_get(attr->ca_owner)) { + error = -ENODEV; +@@ -236,9 +395,14 @@ static int check_perm(struct inode * ino + * and we must have a store method. + */ + if (file->f_mode & FMODE_WRITE) { +- if (!(inode->i_mode & S_IWUGO) || !attr->store) ++ if (!(inode->i_mode & S_IWUGO)) + goto Eaccess; + ++ if ((type & CONFIGFS_ITEM_ATTR) && !attr->store) ++ goto Eaccess; ++ ++ if ((type & CONFIGFS_ITEM_BIN_ATTR) && !bin_attr->write) ++ goto Eaccess; + } + + /* File needs read support. +@@ -246,7 +410,13 @@ static int check_perm(struct inode * ino + * must be a show method for it. + */ + if (file->f_mode & FMODE_READ) { +- if (!(inode->i_mode & S_IRUGO) || !attr->show) ++ if (!(inode->i_mode & S_IRUGO)) ++ goto Eaccess; ++ ++ if ((type & CONFIGFS_ITEM_ATTR) && !attr->show) ++ goto Eaccess; ++ ++ if ((type & CONFIGFS_ITEM_BIN_ATTR) && !bin_attr->read) + goto Eaccess; + } + +@@ -260,6 +430,8 @@ static int check_perm(struct inode * ino + } + mutex_init(&buffer->mutex); + buffer->needs_read_fill = 1; ++ buffer->read_in_progress = 0; ++ buffer->write_in_progress = 0; + buffer->ops = ops; + file->private_data = buffer; + goto Done; +@@ -277,12 +449,7 @@ static int check_perm(struct inode * ino + return error; + } + +-static int configfs_open_file(struct inode * inode, struct file * filp) +-{ +- return check_perm(inode,filp); +-} +- +-static int configfs_release(struct inode * inode, struct file * filp) ++static int configfs_release(struct inode *inode, struct file *filp) + { + struct config_item * item = to_item(filp->f_path.dentry->d_parent); + struct configfs_attribute * attr = to_attr(filp->f_path.dentry); +@@ -303,6 +470,47 @@ static int configfs_release(struct inode + return 0; + } + ++static int configfs_open_file(struct inode *inode, struct file *filp) ++{ ++ return check_perm(inode, filp, CONFIGFS_ITEM_ATTR); ++} ++ ++static int configfs_open_bin_file(struct inode *inode, struct file *filp) ++{ ++ return check_perm(inode, filp, CONFIGFS_ITEM_BIN_ATTR); ++} ++ ++static int configfs_release_bin_file(struct inode *inode, struct file *filp) ++{ ++ struct configfs_buffer *buffer = filp->private_data; ++ struct dentry *dentry = filp->f_path.dentry; ++ struct config_item *item = to_item(dentry->d_parent); ++ struct configfs_bin_attribute *bin_attr = to_bin_attr(dentry); ++ ssize_t len = 0; ++ int ret; ++ ++ buffer->read_in_progress = 0; ++ ++ if (buffer->write_in_progress) { ++ buffer->write_in_progress = 0; ++ ++ len = bin_attr->write(item, buffer->bin_buffer, ++ buffer->bin_buffer_size); ++ ++ /* vfree on NULL is safe */ ++ vfree(buffer->bin_buffer); ++ buffer->bin_buffer = NULL; ++ buffer->bin_buffer_size = 0; ++ buffer->needs_read_fill = 1; ++ } ++ ++ ret = configfs_release(inode, filp); ++ if (len < 0) ++ return len; ++ return ret; ++} ++ ++ + const struct file_operations configfs_file_operations = { + .read = configfs_read_file, + .write = configfs_write_file, +@@ -311,6 +519,14 @@ const struct file_operations configfs_fi + .release = configfs_release, + }; + ++const struct file_operations configfs_bin_file_operations = { ++ .read = configfs_read_bin_file, ++ .write = configfs_write_bin_file, ++ .llseek = NULL, /* bin file is not seekable */ ++ .open = configfs_open_bin_file, ++ .release = configfs_release_bin_file, ++}; ++ + /** + * configfs_create_file - create an attribute file for an item. + * @item: item we're creating for. +@@ -332,3 +548,24 @@ int configfs_create_file(struct config_i + return error; + } + ++/** ++ * configfs_create_bin_file - create a binary attribute file for an item. ++ * @item: item we're creating for. ++ * @attr: atrribute descriptor. ++ */ ++ ++int configfs_create_bin_file(struct config_item *item, ++ const struct configfs_bin_attribute *bin_attr) ++{ ++ struct dentry *dir = item->ci_dentry; ++ struct configfs_dirent *parent_sd = dir->d_fsdata; ++ umode_t mode = (bin_attr->cb_attr.ca_mode & S_IALLUGO) | S_IFREG; ++ int error = 0; ++ ++ mutex_lock_nested(&dir->d_inode->i_mutex, I_MUTEX_NORMAL); ++ error = configfs_make_dirent(parent_sd, NULL, (void *) bin_attr, mode, ++ CONFIGFS_ITEM_BIN_ATTR); ++ mutex_unlock(&dir->d_inode->i_mutex); ++ ++ return error; ++} +--- a/fs/configfs/inode.c ++++ b/fs/configfs/inode.c +@@ -218,7 +218,7 @@ const unsigned char * configfs_get_name( + if (sd->s_type & (CONFIGFS_DIR | CONFIGFS_ITEM_LINK)) + return sd->s_dentry->d_name.name; + +- if (sd->s_type & CONFIGFS_ITEM_ATTR) { ++ if (sd->s_type & (CONFIGFS_ITEM_ATTR | CONFIGFS_ITEM_BIN_ATTR)) { + attr = sd->s_element; + return attr->ca_name; + } +--- a/include/linux/configfs.h ++++ b/include/linux/configfs.h +@@ -51,6 +51,7 @@ struct module; + struct configfs_item_operations; + struct configfs_group_operations; + struct configfs_attribute; ++struct configfs_bin_attribute; + struct configfs_subsystem; + + struct config_item { +@@ -84,6 +85,7 @@ struct config_item_type { + struct configfs_item_operations *ct_item_ops; + struct configfs_group_operations *ct_group_ops; + struct configfs_attribute **ct_attrs; ++ struct configfs_bin_attribute **ct_bin_attrs; + }; + + /** +@@ -154,6 +156,54 @@ static struct configfs_attribute _pfx##a + .store = _pfx##_name##_store, \ + } + ++struct file; ++struct vm_area_struct; ++ ++struct configfs_bin_attribute { ++ struct configfs_attribute cb_attr; /* std. attribute */ ++ void *cb_private; /* for user */ ++ size_t cb_max_size; /* max core size */ ++ ssize_t (*read)(struct config_item *, void *, size_t); ++ ssize_t (*write)(struct config_item *, const void *, size_t); ++}; ++ ++#define CONFIGFS_BIN_ATTR(_pfx, _name, _priv, _maxsz) \ ++static struct configfs_bin_attribute _pfx##attr_##_name = { \ ++ .cb_attr = { \ ++ .ca_name = __stringify(_name), \ ++ .ca_mode = S_IRUGO | S_IWUSR, \ ++ .ca_owner = THIS_MODULE, \ ++ }, \ ++ .cb_private = _priv, \ ++ .cb_max_size = _maxsz, \ ++ .read = _pfx##_name##_read, \ ++ .write = _pfx##_name##_write, \ ++} ++ ++#define CONFIGFS_BIN_ATTR_RO(_pfx, _name, _priv, _maxsz) \ ++static struct configfs_attribute _pfx##attr_##_name = { \ ++ .cb_attr = { \ ++ .ca_name = __stringify(_name), \ ++ .ca_mode = S_IRUGO, \ ++ .ca_owner = THIS_MODULE, \ ++ }, \ ++ .cb_private = _priv, \ ++ .cb_max_size = _maxsz, \ ++ .read = _pfx##_name##_read, \ ++} ++ ++#define CONFIGFS_BIN_ATTR_WO(_pfx, _name, _priv, _maxsz) \ ++static struct configfs_attribute _pfx##attr_##_name = { \ ++ .cb_attr = { \ ++ .ca_name = __stringify(_name), \ ++ .ca_mode = S_IWUSR, \ ++ .ca_owner = THIS_MODULE, \ ++ }, \ ++ .cb_private = _priv, \ ++ .cb_max_size = _maxsz, \ ++ .write = _pfx##_name##_write, \ ++} ++ + /* + * If allow_link() exists, the item can symlink(2) out to other + * items. If the item is a group, it may support mkdir(2). |