fasync_helper

Name:async_helper() is used by almost all character device drivers* to set up the fasync queue, and for regular files by the file* lease code. It returns negative on error, 0 if it did no changes* and positive if it added/deleted the entry.

Proto:int fasync_helper(int fd, struct file *filp, int on, struct fasync_struct **fapp)

Type:int

Parameter:

Type	Parameter	Name
int	fd
struct file *	filp
int	on
struct fasync_struct **	fapp

980

If Not on Then Return Remove a fasync entry. If successfully removed, return* positive and clear the FASYNC flag. If no entry exists,* do nothing and return 0.* NOTE! It is very important that the FASYNC flag always* match the state "is the filp on a fasync list".

982

Return Add a fasync entry. Return negative on error, positive if* added, and zero if did nothing but change an existing one.

**Caller**
Name	Describe
pipe_fasync
fsnotify_fasync
io_uring_fasync
lease_modify	We already had a lease on this file; just change its type

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