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29 .Dt VOP_READ_PGCACHE 9
40 .Fa "struct vnode *vp"
43 .Fa "struct ucred *cred"
46 This entry point reads the contents of a file.
47 The intent is to provide the data from caches, which do not require
48 expensive operations or any disk IO.
49 For instance, if filesystem uses normal VM page cache and maintains
52 .Xr vn_read_from_obj 9
53 helper to return data from the resident
57 The filesystem indicates support for the
59 on specific vnode by setting the
64 The function does not need to satisfy the whole request; it also might choose
65 to not provide any data.
68 must be advanced by the amount of read data,
72 and VFS would handle the rest of the read operation using the
75 The VFS layer does the same deadlock avoidance for accessing userspace
81 Vnode is not locked on the call entry and should not be locked on return.
82 For a filesystem that requires vnode lock to return any data, it does
83 not make sense to implement
87 flag) since VFS arranges the call to
92 .Bl -tag -width ioflag
94 The vnode of the file.
96 The location of the data to be read.
102 The credentials of the caller.
106 does not handle non-zero
110 The file should be referenced on entry on entry and will still be
112 Rangelock covering the whole read range should be owned around the call.
114 Zero is returned on success, when the whole request is satisfied, and no
115 more data cannot be provided for it by any means.
116 If more data can be returned, but
118 was unable to provide it,
123 records should be updated according to the partial operation done.
125 Otherwise an error code is returned,