Hi,
I'm new to this area so please excuse some naive questions.
I have no criticisms, just desire clarifications on your
"Families" API for EA.
I've been looking at your API versus the XFS attrib functionality.
1.
It seems that your EA API assumes EA lists, whereas
in XFS we seem to base it on EA sets.
That is, in your API the ordering of attributes is significant;
hence the ATR_APPEND, ATR_PREPEND and an ATR_SET definition which
mentions the handling of multiple instances of the same name.
In XFS there doesn't seem to be an explicit concept of ordering,
and I thought that only one attribute name could exist for
a particular file system object (well actually 2 - possibly
a User space version and a Root space version) -
is this not the case, Curtis ?
2.
In your definitions, you mention how only "name" in <new> is
used for GET, and in SET you mention,
"if multiple instances of the name already exist".
I assume that your reference to name existence really means
matching on <name, attrib_family, name_family> ?
3.
How do you remove an attribute or multiple attributes ?
Do you do a SET with a null value in <new> ?
Thanks muchly,
Tim.
Stephen wrote:
=====================================================================
Our proposed kernel API looks something like this:
sys_setattr (char *filename, int attrib_family, int op,
struct attrib *old_attribs, int *old_lenp,
struct attrib *new_attribs, int new_len);
sys_fsetattr(int fd, int attrib_family, int op,
struct attrib *old_attribs, int *old_lenp,
struct attrib *new_attribs, int new_len);
where <op> can be
ATR_SET overwrite existing attribute
ATR_GET read existing attribute
ATR_GETALL read entire ordered attribute list (ignores new val)
ATR_PREPEND add new attribute to start of ordered list
ATR_APPEND add new attribute to end of ordered list
ATR_REPLACE replace entire ordered attribute list
and where <attribs> is a buffer of length <len> bytes of variable
length struct attrib records:
struct attrib {
int rec_len; /* Length of the whole record:
should be padded to long
alignment */
int name_family; /* Which namespace is the name in? */
int name_len;
int val_len;
char name[variable]; /* byte-aligned */
char val[variable]; /* byte-aligned */
};
ATR_SET will overwrite an existing attribute, or if the attribute does
not already exist, will append the new attribute (ie. it does not
override existing ACL controls, in keeping with the Principle of Least
Surprise). If multiple instances of the name already exist, then the
first one is replaced and subsequent ones deleted. If supplied with
an "old" buffer, all old attributes of that name will be returned.
For the PREPEND/APPEND/REPLACE operations, the entire old attribute
set is returned.
For GET, the <new> specification is read and all attributes which
match any items in <new> are returned, in the order in which they are
specified in <new>. The actual value in <new> is ignored; only the
name is used.
For GETALL, <new> is ignored entirely.
*old_lenp should contain the size of the old attributes buffer on
entry. It will contain the number of valid bytes in the old buffer on
exit. If the buffer is not sufficiently large to contain all of the
attributes, E2BIG is returned.
=====================================================================
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