Hi, I am not expert on kernel link internals, but if you need/prefer atomic change to a specific link, does my log [1] below suggest a way?
On +2022-06-03 21:30:39 +0200, Ludovic Courtès wrote: > Hi, > > Maxime Devos <maximede...@telenet.be> skribis: > > >, Maybe replace > > > > (symlink target pivot) > > > > by (symlink/remove-old target pivot) > > > > where > > > > (define (symlink/remove-old target link) > > "Make a symbolic link named LINK pointing to TARGET. > > If LINK already exists, it will be removed first. > > This is not an atomic operation." > > (catch 'system-error > > (lambda () > > (symlink target link)) > > (lambda stuff > > (if (= (system-error-errno stuff) EEXIST) > > (begin > > ;; remove old link and retry > > (delete-file link) > > (symlink/remove-old link target)) > > (apply throw stuff))))) > > Alright, SGTM (this procedure would be kept private). > > So Arun, the floor is yours! :-) > > Ludo’. > [0]: (some "<--= note" notes edited in) BTW: notice that Size: is number of chars in TARGET name, not the LINK name --8<---------------cut here---------------start------------->8--- $ ln -sT TARGET LINK $ stat LINK File: LINK -> TARGET Size: 6 Blocks: 0 IO Block: 4096 symbolic link Device: fe00h/65024d Inode: 19401553 Links: 1 # <--= note inode number: mv will not change it Access: (0777/lrwxrwxrwx) Uid: ( 1000/ bokr) Gid: ( 1000/ bokr) Access: 2022-06-04 00:57:47.680832044 +0200 Modify: 2022-06-04 00:57:47.680832044 +0200 Change: 2022-06-04 00:57:47.680832044 +0200 Birth: - $ mv -v LINK WAS-LINK renamed 'LINK' -> 'WAS-LINK' $ stat WAS-LINK File: WAS-LINK -> TARGET Size: 6 Blocks: 0 IO Block: 4096 symbolic link # <--= TARGET is still 6 chars :) Device: fe00h/65024d Inode: 19401553 Links: 1 # <--= note inode number: did not change with mv Access: (0777/lrwxrwxrwx) Uid: ( 1000/ bokr) Gid: ( 1000/ bokr) Access: 2022-06-04 00:57:47.680832044 +0200 Modify: 2022-06-04 00:57:47.680832044 +0200 Change: 2022-06-04 00:58:33.617240104 +0200 Birth: - $ ln -sT NEW-TARGET LINK $ stat LINK File: LINK -> NEW-TARGET Size: 10 Blocks: 0 IO Block: 4096 symbolic link # <--= NEW-TARGET is 10 chars :) Device: fe00h/65024d Inode: 19401638 Links: 1 <--= note inode number: new for new use of LINK name Access: (0777/lrwxrwxrwx) Uid: ( 1000/ bokr) Gid: ( 1000/ bokr) Access: 2022-06-04 01:00:10.630121441 +0200 Modify: 2022-06-04 01:00:10.630121441 +0200 Change: 2022-06-04 01:00:10.630121441 +0200 Birth: - $ rm -v WAS-LINK <--= note no OS objection to removing renamed old LINK removed 'WAS-LINK' $ stat *LINK* File: LINK -> NEW-TARGET Size: 10 Blocks: 0 IO Block: 4096 symbolic link Device: fe00h/65024d Inode: 19401638 Links: 1 Access: (0777/lrwxrwxrwx) Uid: ( 1000/ bokr) Gid: ( 1000/ bokr) Access: 2022-06-04 01:00:10.630121441 +0200 Modify: 2022-06-04 01:00:10.630121441 +0200 Change: 2022-06-04 01:00:10.630121441 +0200 Birth: - $ --8<---------------cut here---------------end--------------->8--- I'm guessing the inode rewrite involved in mv -v LINK WAS-LINK should be atomic? Maybe some kernels have to struggle without good hardware support, but still atomic? Maybe a kernel insider will chime in? HTH some way. -- Regards, Bengt Richter
