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CIFS: document tcon/ses/server refcount dance 

Signed-off-by: Aurelien Aptel <aaptel@suse.com>
Signed-off-by: Steve French <smfrench@gmail.com>
Reviewed-by: Ronnie Sahlberg <lsahlber@redhat.com>
This commit is contained in:
Aurelien Aptel 2018-01-25 18:47:52 +01:00 committed by Steve French
parent 6b314714ff
commit 4a1360d01d
1 changed files with 31 additions and 1 deletions
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32
fs/cifs/connect.c
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@ -2704,6 +2704,13 @@ cifs_set_cifscreds(struct smb_vol *vol __attribute__((unused)),
}
#endif /* CONFIG_KEYS */
/**
* cifs_get_smb_ses - get a session matching @volume_info data from @server
*
* This function assumes it is being called from cifs_mount() where we
* already got a server reference (server refcount +1). See
* cifs_get_tcon() for refcount explanations.
*/
static struct cifs_ses *
cifs_get_smb_ses(struct TCP_Server_Info *server, struct smb_vol *volume_info)
{
@ -2877,6 +2884,26 @@ cifs_put_tcon(struct cifs_tcon *tcon)
cifs_put_smb_ses(ses);
}
/**
* cifs_get_tcon - get a tcon matching @volume_info data from @ses
*
* - tcon refcount is the number of mount points using the tcon.
* - ses refcount is the number of tcon using the session.
*
* 1. This function assumes it is being called from cifs_mount() where
* we already got a session reference (ses refcount +1).
*
* 2. Since we're in the context of adding a mount point, the end
* result should be either:
*
* a) a new tcon already allocated with refcount=1 (1 mount point) and
* its session refcount incremented (1 new tcon). This +1 was
* already done in (1).
*
* b) an existing tcon with refcount+1 (add a mount point to it) and
* identical ses refcount (no new tcon). Because of (1) we need to
* decrement the ses refcount.
*/
static struct cifs_tcon *
cifs_get_tcon(struct cifs_ses *ses, struct smb_vol *volume_info)
{
@ -2885,8 +2912,11 @@ cifs_get_tcon(struct cifs_ses *ses, struct smb_vol *volume_info)
tcon = cifs_find_tcon(ses, volume_info);
if (tcon) {
/*
* tcon has refcount already incremented but we need to
* decrement extra ses reference gotten by caller (case b)
*/
cifs_dbg(FYI, "Found match on UNC path\n");
/* existing tcon already has a reference */
cifs_put_smb_ses(ses);
return tcon;
}